ARM: dts: imx51-babbage: Add USB OTG support

Tested by pinging from the host PC to the imx51-babbage via a g_ether
connection.

Signed-off by: Dave Ebright <dave.ebright@parsons.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>