arch/arm/src/imxrt:  Add missing support for the Cortex-M7 caches; configs/imxrt1050-evk:  Enable I- and D-Caches in the nsh configuration.  Calibrate the delay loop.  Add support for the on-board LED.

 arch/arm/src/imxrt/imxrt_serial.c:  Fix some interrupt instabilities; must be in a critical section when modifying serial interrupts.  configs/imxrt1050-evk/nsh/defconfig:  Use the BASEPRI register to enable/disable interrupts; enable the PROCFS file system.

configs/photon: Fixes build error introduced in recent rgbled changes.

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

Photon rgbled fix

* configs/photon: Simplifies RGB led start-up logic.

* configs/photon: RGB led on Photon is common anode. CONFIGS_RGBLED_INVERT is now enabled

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

rgbled: Fixes led issues caused by uninitialized memory with CONFIG_RGBLED_MULTICHAN.

The uninitialized pwm_info_s struct caused a rogue channel to be started causing errros in the pwm driver

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

net/udp:  Associated with last commit.  Make sure that the new connection flag is cleared when a new UDP connection structure is allocated.

In connection-mode UDP sockets, a remote address is retained in the UDP connection structure.  This determines both there send() will send the packets and which packets recv() will accept.

This same mechanism is used for connection-less UDP sendto:  A temporary remote address is written into the connection structure to support the sendto() operation.  That address persists until the next recvfrom() when it is reset to accept any address.

When UDP read-ahead buffering is enabled, however, that means that the old, invalid remote address can be left in the connection structure for some time.  This can cause read-ahead buffer to fail, dropping UDP packets.

Shortening the time between when he remote address is reset (i.e., immediately after the sendto() completes) is not a solution, that does not eliminate the race condition; in only makes it smaller.

With this change, a flag was added to the connection structure to indicate if the UDP socket is in connection mode or if it is connection-less.  This change effects only UDP receive operations:  The remote address in the UDP connection is always ignored if the UDP socket is not in connection-mode.

No for connection-mode sockets, that remote address behaves as before.  But for connection-less sockets, it is only used by sendto().

arch/arm/src/kinetis + SDHC configs:  Make Kinetis SDHC pullups work the same as the STM32 SDIO pullups

arch/arm/src/stm32: Add internal pull-up option for SDIO pins (also picks up an unrelated change to a README.txt file)

LibTargets.mk, tools/Config.mk:  Drop executable bit on installed libraries. The rules to install libraries under lib/ were modified to use mode 0644 instead of the default 0755.

Documentation/NuttShell.html:  Document the mkfatfs the -r option which can be used to specify the number of entries in the FAT12/FAT16 root directory.

Back out part of f4bcaa4f.If CONFIG_ARCH_IDLE_CUSTOM is defined, then it should not use the version of lc823450_idle.c in arch/arm/src/lc823450. That part was correct before the PR. If CONFIG_ARCH_IDLE_CUSTOM, then the build should use a custom IDLE loop in the board src/ directory.

arch/arm/src/lc823450: Fix some recently introduced build issues

Reported-by: Wig Cheng <wig.cheng@relajet.com>
Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

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

Clean up some spacing in the last commit... Seemed like a good idea at the time, but it is better to be consisten than better.

libc/unistd:  Initial, minimal implementation of sysconf().  Only sufficient to support the functionality of less standard getdtabilesize().

Squashed commit of the following:

    configs/*/README.txt: Replace each occurrence of './configure.sh' with 'tools/configure.sh'
    configs/*/README.txt:  Remove 'cd ..' after each './configure.sh'
    configs/*/README.txt:  Remove 'cd -' after each './configure.sh'
    configs/*/README.txt:  Remove 'cd tools' before each './configure.sh'
    configs/README.txt:  Remove instruction to CD tools/ before running configure.sh.

configs/teensy-3.x/usbnsh:  Remove CONFIG_USBDEV_DUALSPEED from configuration.  Hardware supports only FS.

arch/arm/src/lpc17xx:  Add support for ARMv7-M run time stack checking on NXP LPC17xx MCUs based on CONFIG_ARMV7M_STACKCHECK. Basically copied from stm32.

configs/freedom-k28f:  If drivers/leds/rgbled.c is enabled, then treat the board as though it had no discrete LEDs.

drivers/leds/rgbled.c:  Fix a compilation error introduced with a recent change to add multi-channel operation to RGB LED driver.

configs/freedom-k28f:  With these changes to the configuration, the NSH configuration is now functional on the k28f board.  Also fixes corrects the active logic level for the RGB LED.   arch/arm/src/kinetis/chip:  Fixes an error in vector configuration.

arch/arm/src/nrf52/nrf52_flash.c:  Add missing erasesize method.  Add missing function header comments.

libc/libc.csv: Fix missing or duplicate quotation marks.  mksymtab was not able to parse libc/libc.csv due to missing or duplicate quotation marks.