mm: implement ->map_pages for shmem/tmpfs

mm: implement ->map_pages for shmem/tmpfs

In shmem/tmpfs, we also use the generic filemap_map_pages, seems the
additional checking is not worth a separate version of map_pages for it.

Signed-off-by: Ning Qu <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Dave Chinner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>