powerpc: purge all the prefetched instructions for the coherent icache flush

As Benjamin Herrenschmidt has indicated, we still need a dummy icbi to
purge all the prefetched instructions from the ifetch buffers for the
snooping icache. We also need a sync before the icbi to order the
actual stores to memory that might have modified instructions with
the icbi.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

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

diff --cc arch/powerpc/kernel/misc_32.S
Simple merge

diff --cc arch/powerpc/kernel/misc_64.S
Simple merge