Make various things static

Building an allnoconfig kernel, sparse asked whether these could be
static, so I checked, and they are only used in the file where they are
declared.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>