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