imx: ventana: add GW5913 support

imx: ventana: add GW5913 support

The GW5913 is a Single Board Computer based on the NXP i.MX6Q/DL SoC
with the following features:
 - DDR3 DRAM
 - NAND FLASH (256MiB or 2048MiB)
 - Gateworks System Periperhal Controller
 - front panel LED's
 - front panel pushbutton
 - Digital I/O connector (I2C/GPIO/UART)
 - u-blox Zoe-M8Q GPS
 - 1x RJ45 GbE
 - 1x MiniPCIe socket with PCIe USB 2.0 and nanoSIM socket
 - Passive PoE and wide-range DC power supply

Signed-off-by: Tim Harvey <tharvey@gateworks.com>