mm: page-flags: clean up the page flag test, set, clear macros

- PAGEFLAG_FALSE only defines TEST, make it define SET and CLEAR as
  well, analogous to PAGEFLAG.

- Define TESTSETFLAG_FALSE, analogous to TESTSETFLAG.

- Define TESTSCFLAG_FALSE, analogous to TESTSCFLAG

- Make PG_mlocked accessors the same on both MMU and !MMU setups

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>