page flags: add PAGEFLAGS_FALSE for flags that are always false

Turns out that there are a number of times that a flag is simply always
returning 0.  Define a macro for that.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>