imx6: add support for gw52xx

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
 * 2x PCIe
 * 1x USB EHCI (to PCIe socket2)
 * 1x USB OTG (to front panel or PCIe socket1)
 * 1x uSD
 * LVDS
 * HDMI AudioVideo out
 * Analog Video in
 * Digital IO
 * Gateworks System Controller

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

SVN-Revision: 38425