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

Basic Support for STM32L476 MDK Board

The Motorola MDK is based off of an earlier version
of NuttX.  This only provides a basic nsh shell.

Signed-off-by: Jim Wylder <jwylder@motorola.com>

For STM32L4 parts, the higher number USART ports supported
varies.  Add the HAVE_USARTx definitions to the configuration
to allow enabling the higher numbered USART ports.

Signed-off-by: Jim Wylder <jwylder@motorola.com>

restore stm32l4 name

Register renames to allow stm32l4 usb device compilation

Upstream_to_greg