mm: make page_lock_anon_vma() static

page_lock_anon_vma() and page_unlock_anon_vma() were made available to
show_page_path() in vmscan.c; but now that has been removed, make them
static in rmap.c again, they're better kept private if possible.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>