[ARM] Move FLUSH_BASE macros to asm/arch/memory.h

FLUSH_BASE must be visible to arch/arm/mm/init.c in order for the
memory region to be setup.  Move these definitions from
asm-arm/arch-*/hardware.h into asm-arm/arch-*/memory.h where mm
stuff can see them.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>