powerpc/mm: Don't call __flush_dcache_icache_phys() with PA>VA

__flush_dcache_icache_phys() requires the ability to access the
memory with the MMU disabled, which means that on a 32-bit system
any memory above 4 GiB is inaccessible.  In particular, mpc86xx is
32-bit and can have more than 4 GiB of RAM.

Signed-off-by: Scott Wood <scottwood@freescale.com>

diff --cc arch/powerpc/include/asm/cacheflush.h
Simple merge

diff --cc arch/powerpc/mm/mem.c
Simple merge