mm: Add and use update_mmu_cache_pmd() in transparent huge page code.

The transparent huge page code passes a PMD pointer in as the third
argument of update_mmu_cache(), which expects a PTE pointer.

This never got noticed because X86 implements update_mmu_cache() as a
macro and thus we don't get any type checking, and X86 is the only
architecture which supports transparent huge pages currently.

Before other architectures can support transparent huge pages properly we
need to add a new interface which will take a PMD pointer as the third
argument rather than a PTE pointer.

[akpm@linux-foundation.org: implement update_mm_cache_pmd() for s390]
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>