STM32L4 DFSDM: add peripheral, DAC, TIM: small changes

* STM32L4 DAC: do not configure output pin if it is not used

* STM32L4 TIM: fix compilation of timers with complementary outputs when not PWM_MULTICHAN

* STM32L4 DFSDM: peripheral for digital filters for sigma-delta ADCs

    Initial version. Timer trigger support is not completed and there is
    some issue with DMA.

Approved-by: Gregory Nutt <gnutt@nuttx.org>

sched/env_dup.c:  Fix an error in the duplication of the child tasks environment in the special case where the parent's environment was created, but then all of the variables were unset.  In that case, there is still an allocation in place but the size of the allocation is zero.  This case was not being handled correctly when a child task attempts to create its environment and inherit the zero-size partent environment.  Noted by Anthony Merlino.

Add driver for APA102 LED controller.  These LEDs are used on LED Strips and are controlled over SPI.

Networking: sockgetname() files need to include udp/udp.h and tcp/tcp.h or otherwise NET_UDP_HAVE_STACK and NET_TCP_HAVE_STACK are undefined and the logic is never compiled.  Noted by Anthony Merlino

configs/stm32f4discovery: Update README.  Add summary of differences with the newest STM32F407G-DISC1 part.  Remove a lot of old discussion that is really no longer helpful.

    stm3240g-eval:  Add a configuration for testing the FB character driver at drivers/video/fb.c using the LCD frame driver front end at drivers/lcd/lcd_framebuffer.c.  Appears to be fully functional.

    stm3240g-eval:  Replace the old-style stm32_appinit.c with tne new one from the STM32F4-Discovery

    stm3240g-eval:  Rename stm32_appinit.c to stm32_bringup.c to better match other architectures

Fix some cosmetic stuff in the framebuffer character driver and in the LCD framebuffer driver front-end.

    configs/stm3210e-eval: Bring in new stm32_appinit.c, add board_initialize(), add support for FB character driver.
    configs/stm3210e-eval: Rename stm32_appinit.c to stm32_bringup.c so that the start up logic is compatible with other, new boards.

SAMv71-XULT:  Add a configuration to test the LCD framebuffer driver.  Not quite yet working properly.

drivers/lcd:  Add suppose for a generic front-end that will convert any LCD driver into a framebuffer driver.

    drivers/video:     fb driver now clears framebuffer initially.  Eliminates (or minimizes) initial garbage on the display.
    configs/open1788:  Initialization now follows the pattern of other boards.  Add initialization of fb driver.
    configs/open1788:  Add a configuration for testing the framebuffer driver.

STM32 Tickless: The attached patch removes the restriction to 16bit counts when a 32bit timer is used for the new tickless on the stm32. As it is now, the restriction is very limiting, especially if one wants high granularity and large achievable intervals and has the hardware (namely the 32bit timers) available.

drivers/xbee: Fixes a few warnings

* drivers/xbee: Fixes a few warnings

* configs/clicker2-stm32: Updates sections about i8sak usage in the README

Approved-by: Gregory Nutt <gnutt@nuttx.org>

drivers/wireless:  Adds XBee S2C (802.15.4 firmware) support. XBee driver emulates mac802154 interface

* drivers/wireless/xbee: Adds xbee_netdev. Very similar to mac802154_netdev

* configs/same70-xplained: Starts adding support for XBee radio

* drivers/wireless/ieee802154/xbee: More structuring of XBee driver

* drivers/wireless/ieee802154/xbee: More Xbee work. Starts adding support on Clicker2

* drivers/wireless/ieee802154/xbee: More XBee MAC code

* configs/clicker2-stm32: More work to add XBee radio support

* drivers/wireless/ieee802154/xbee: Most of driver is now structured. No build errors

* configs/clicker2-stm32: Adjustments to XBee click module support

* drivers/xbee: Changes md_ prefix to xd_ prefix for xbeenet_driver_s fields

* drivers/xbee: XBee network device now passes MAC events via IOCTL

* drivers/xbee: Support querying device for parameters, setting parameters, and structures association/startpan logic

* configs/clicker2-stm32: Fixes Xbee lower half ATTN poll logic

* drivers/xbee: Removes dependce on CONFIG_IEEE802154_NETDEV

* drivers/xbee: Supports MAC RESET.request primitive

* drivers/xbee: Exposes generic AT query to the rest of driver

* drivers/xbee: Sets local values when writing setting change to Xbee device

* drivers/xbee: Finish association logic

* drivers/xbee: Adds xbee_get_mhrlen( ) allocating enough space for API frame header to frame

* drivers/xbee: Finishes transmit/receive logic

* drivers/xbee: Fixes xbee_netdev to match logic in mac802154_netdev.c

* drivers/xbee: Rearranges logic to prevent a loop condition where recursion could potentially occur to the point of deadlocking the system

Approved-by: Gregory Nutt <gnutt@nuttx.org>

    Merged in merlin17/nuttx/mac802154-sock (pull request #479)

    wireless/ieee802154: Adds support for receiving MAC events via IOCTL through socket interface. Other small fixes and cleanup

    * ioctl: Cleans up MAC802154IOC values
    * wireless/ieee802154: Cleans up MAC802154IOC_NOTIFY_REGISTER logic in character driver
    * wireless/ieee802154/mac802154_netdev:  Adds support for MAC event notification via IOCTL
    * wireless/ieee802154/mac802154: Changes reset logic. No longer reset extended address.
    * wireless/ieee802154: Cleans up MAC802154IOC logic

        Moves MAC802154IOC from ieee802154_ioctl.h and renames ieee802154_ioctl.h to ieee802154_device.h since it only contains types relevant to the MAC char device now.

    * wireless/ieee802154/mac802154_device: Cleans up IOCTL logic for recent changes.
    * drivers/wireless/ieee802154/mrf24j40: Adds missing break in case statement
    * wireless/ieee802154/mac802154_netdev: Starts adding support for passing MAC events via IOCTL
    * wireless/ieee802154/mac802154: Fixes issue with receiver enable logic
    * wireless/ieee802154/mac802154: Fixes issue where extended address is cleared and not rewritten after radio reset
    * configs/clicker2-stm32/mrf24j40-mac: Enables RAMLOG and wireless driver logging
    * wireless/ieee802154/mac802154: Fixes poll logic meant to automatically choose address mode based on short address range.

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Added initialization code and Kconfig entries for LIS3DSH accelerometer on STM32F4Discovery + associated changes to LIS3DSH driver

Approved-by: Gregory Nutt <gnutt@nuttx.org>

driver on STM32F4Discovery rev. C boards and attach the associated interrupt callback.

Added the argument parameter (FAR void *arg) to the interrupt handler provided by the LIS3DSH
driver to fit the definition for ISRs in xcpt_t.

Changed the check for working queue availability in lis3dsh interrupt handler to use work_available()
and not crash in case of an overrun.