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