imx6: add Gateworks GW551x support

imx6: add Gateworks GW551x support

Upstream patch: e9d6d6b62f306ba83e1441af5daf2809a6167474

Add support for the Gateworks GW5510 board featuring:
 * i.MX6 SoC
 * up to 512MB DDR3
 * up to 2GB NAND flash
 * 1x miniPCIe socket (with USB)
 * HDMI out (micro-HDMI)
 * HDMI in (micro-HDMI) (currently supported by only vendor kernel)
 * TTL level I/O (supported by GW16111 breakout board):
  * I2C
  * 2x UART
  * CAN
  * 2x DIO (GPIO/PWM)
  * USB OTG

Also add support to OpenWrt build system

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Pushpal Sidhu <psidhu@gateworks.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47505 3c298f89-4303-0410-b956-a3cf2f4a3e73