powerpc/mm/thp: Remove code duplication

Rename invalidate_old_hpte to flush_hash_hugepage and use that in
other places.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

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

diff --cc arch/powerpc/mm/hash_utils_64.c
Simple merge

diff --cc arch/powerpc/mm/hugepage-hash64.c
Simple merge

diff --cc arch/powerpc/mm/pgtable_64.c
Simple merge