mm/hmm: factor out pte and pmd handling to simplify hmm_vma_walk_pmd()

mm/hmm: factor out pte and pmd handling to simplify hmm_vma_walk_pmd()

No functional change, just create one function to handle pmd and one to
handle pte (hmm_vma_handle_pmd() and hmm_vma_handle_pte()).

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Jérôme Glisse <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Cc: Evgeny Baskakov <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Mark Hairgrove <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>