mx31moboard: OTG host support for smartbot board

The Eyebot robot needs the OTG port in host mode on the smartbot.

Add a new board definition so we can select the usb host/device
mode at boot with the mx31moboard_baseboard boot parameter.

Signed-off-by: Philippe Rétornaz <philippe.retornaz@epfl.ch>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>