mm: add PageAnonNotKsm()

mm: add PageAnonNotKsm()

Check that this anonymous page is really anonymous, not anonymous-or-KSM.
This optimises the debug check, but its real purpose is to remove the last
two users of PageKsm().

[willy@infradead.org: fix assertions]
Link: https://lkml.kernel.org/r/ZwApWPER7caIA_N3@casper.infradead.org
Link: https://lkml.kernel.org/r/20241002152533.1350629-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alex Shi <alexs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>