ARM: dts: imx6: Add support for imx6q wandboard

Add support for the imx6q wanboard variant.

Since imx6q/dl are pin to pin compatible, introduce the imx6qdl-wandboard.dtsi
file that contains the common peripheral nodes.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>