arm/mx5: add device tree support for imx51 babbage

It adds device tree support for imx51 babbage board.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>