ARM: dts: add initial Rex Pro board support

Add initial Rex Pro i.mx6q board support. Ethernet, UART, USB, I2C, SPI, HDMI,
Audio, and SDHC cards are working.  Currently no mainline u-boot, so boot with
cat zImage imx6q-rex-pro.dtb > zImage.dtb, then using mkimage create uImage

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>