[ARM] 4718/1: Fix redefinition warnings in PXA uncompressor code

FFUART and friends are already defined as __REG(x) in pxa-regs.h.
Instead of redefining them here, we can just provide the __REG macro.
Including asm/arch/hardware.h is not an option because this physical
addresses are needed here.
This is a fix for the compiler warnings generated by 4663/1.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>