imx6: add support for gw54xx

imx6: add support for gw54xx

The Gateworks GW54xx family of products is based on the Freescale
i.MX6Q SoC and offers a large variety of peripherals such as:

  - i.MX6Q 1GB DDR3 (standard)
  - 256MB NAND FLASH (standard)
  - 6x PCIe (3x with USB)
    - Optional expansion for additional USB/PCI based periperhals
  - 1x USB EHCI
  - 1x USB OTG
  - HDMI Audio/Video in/out
  - Analog Video in/out
  - Analog Audio in/out
  - Gateworks System Controller

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38188 3c298f89-4303-0410-b956-a3cf2f4a3e73