ARM: fix PXA build by defining UP2OCR

U-Boot does not currently build for PXA platforms with USB support
enabled:

usb.c:46: error: 'UP2OCR' undeclared (first use in this function)

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Markus Klotzbuecher <mk@denx.de>

Edited commit message.
Signed-off-by: Wolfgang Denk <wd@denx.de>