ARM: dts: imx: Add GW5913 board support

The Gateworks GW5913 is an IMX6 SoC based single board computer with:
 - IMX6Q or IMX6DL
 - 32bit DDR3 DRAM
 - FEC GbE RJ45 front-panel
 - 1x miniPCIe socket with PCI Gen2, USB2
 - 1x miniPCIe socket with PCI Gen2, USB2, nanoSIM
 - 6V to 60V DC input connector
 - GPS (ublox ZOE-M8Q)
 - bi-color front-panel LED
 - 256MB NAND boot device
 - nanoSIM socket
 - user pushbutton
 - Gateworks System Controller (hwmon, pushbutton controller, EEPROM)

Signed-off-by: Robert Jones <rjones@gateworks.com>
Reviewed-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>