kbuild: install kernel-page-flags.h

Programs using /proc/kpageflags need to know about the various flags.  The
<linux/kernel-page-flags.h> provides them and the comments in the file
indicate that it is supposed to be used by user-level code.  But the file
is not installed.

Install the headers and mark the unstable flags as out-of-bounds.  The
page-type tool is also adjusted to not duplicate the definitions

Signed-off-by: Ulrich Drepper <drepper@gmail.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>