mx31moboard: camera support

We have two mt9t031 cameras that have a muxed bus on the robot.
Only one is currently initialized because of limitations in
soc_camera that should be removed later.

Signed-off-by: Valentin Longchamp <valentin.longchamp@epfl.ch>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>