mx5: enable usb gadget for freescale mx51 babbage board

This patch enables usb gadget for freescale mx51 babbage hw. By default,
the OTG port will be in device mode. To put the OTG port into Host mode,
pass "otg_mode=host" in the exec command.

This patch applies to 2.6.34-rc7.

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>