imx6: add support for gw51xx

The Gateworks GW51xx family of products is based on the Freescale
i.MX6DL SoC and offers a small form-factor with peripherals such as:

 - i.MX6DL 512MB DDR3
 - 256MB NAND FLASH
 - 1x PCIe
 - 1x USB EHCI (to PCIe socket)
 - 1x USB OTG
 - HDMI out
 - Analog Video in
 - Gateworks System Controller

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

SVN-Revision: 38189