[POWERPC] 83xx: Added new dr_mode property for usb controller on 83xx

Added a new dr_mode property to describe what mode the DR controller is being
used in (host, device, OTG).  Updated the MPC8349E MDS dts with this new property.

Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>