Add support for quadrature encoders on STM32L4, including gpio definitions for both directions of timer channels.

sched/pthread and task:  When a pthread is started, there is a small bit of logic that will run on the thread of execution of the new pthread.  In the case where the new pthread has a lower priority than the parent thread, then this could cause both the parent thread and the new pthread to be blocked at the priority of the lower priority pthread (assuming that CONFIG_PRIORITY_INHERITANCE is not selected).

This change temporarily boosts the priority of the new pthread to at least the priority of the new pthread to at least the priority of the parent thread.  When that bit of logic has executed on the thread of execution of the new pthread, it will then drop to the correct priority (if necessary) before calling into the new pthread's entry point.

There are some small problems in LPC43xx RS485 mode configuration. In particular: 1. UART0,2,3 do not have DTR pins (different from UART1), so, Kconfig needs to be adjusted. 2. lpc43_uart.c in RS485 mode only configures DIR pin, but doesn't enable pin output for UART0,2,3. 3. should be option to reverse DIR control pin output polarity. 4. lpc43xx/chip/lpc43_uart.h doesn't have USART3 definitions.  NOTE: I didn't modified and didn't tested USART1, as it has different hardware.  From Vytautas Lukenskas.

Add a new ioctl command (set MAXPOS) for tiva QEI

Fix calculations using MSEC_PER_TICK.  If USEC_PER_TICK is less than 1000, then MSEC_PER_TICK will be zero.  It will be inaccurate in any case.

libnx/nxglib: Fix handling of near-horizontal lines of width 1 in nxgl_splitline().  Missing handling for degenerate condition caused width 1 lines such as (0, 0) - (100, 10) to have gaps in the drawing.

Corrects a bad assertion noted by Pierre-noel Bouteville.  Also fixes a reference counting problem in an error condition:  When the mountpoint inode is found but is not an appropriate mountpoint, the reference count on the inode was not being decremented.

Remove GPIO_ETH_RMII_TX_CLK. TX_CLK is not present in RMII +  sched/: Define 'group' even if HAVE_GROUPID is not set

Add QEI lower-half driver impl. for Tiva series chip

SAM3/4: Fix GPIO pull-up/down code.

Enabling the pull-down resistor while the pull-up resistor is still enabled
is not possible. In this case, the write of PIO_PPDER for the relevant I/O
line is discarded. Likewise, enabling the pull-up resistor while the
pull-down resistor is still enabled is not possible. In this case, the
write of PIO_PUER for the relevant I/O line is discarded.

All SAM Ethernet Drivers: Add support so that the drivers can be built with CONFIG_NET_MULTIBUFFER=y

drivers/sensors: Adds support for the  Sensixs XEN1210 3D-boar.  This sensor is used on NANOSATC-BR2 a Brazillian CUBESAT project.

include/nuttx/modem:  Move all modem-related IOCTL commands to a common file to assure that they will be unique