Add support for USB on PSC3 for the mpc5200

Support USB on PSC3 on the mpc5200.  Before this patch, enabling USB support
would reconfigure PSC4 and PSC5 to USB.  The mpc5200 does not support USB
enabled on both the standard USB port and PSC3.  This patch masks the
appropriate bits when enabling USB.

Signed-off-by: Eric Millbrandt <emillbrandt@dekaresearch.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Remy Bohmer <linux@bohmer.net>
diff --git a/README b/README
index cf3867d..246ae2b 100644
--- a/README
+++ b/README
@@ -858,9 +858,13 @@
 		MPC5200 USB requires additional defines:
 			CONFIG_USB_CLOCK
 				for 528 MHz Clock: 0x0001bbbb
+			CONFIG_PSC3_USB
+				for USB on PSC3
 			CONFIG_USB_CONFIG
 				for differential drivers: 0x00001000
 				for single ended drivers: 0x00005000
+				for differential drivers on PSC3: 0x00000100
+				for single ended drivers on PSC3: 0x00004100
 			CONFIG_SYS_USB_EVENT_POLL
 				May be defined to allow interrupt polling
 				instead of using asynchronous interrupts