powerpc/85xx: Update USB device tree status based on pin settings

For P3060 and P4080, USB pins are multiplexed with other functions.
Update the device tree status for USB ports based on setting of
RCW[EC1] & RCW[EC2] which describe if pins are muxed to usb.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>