mm/thp: remove pmd_huge_split_prepare()

mm/thp: remove pmd_huge_split_prepare()

Instead of marking the pmd ready for split, invalidate the pmd.  This
should take care of powerpc requirement.  Only side effect is that we
mark the pmd invalid early.  This can result in us blocking access to
the page a bit longer if we race against a thp split.

[[email protected]: rebased, dirty THP once]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Aneesh Kumar K.V <[email protected]>
Signed-off-by: Kirill A. Shutemov <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: David Daney <[email protected]>
Cc: David Miller <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vineet Gupta <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>