mm: separate out FOLIO_FLAGS from PAGEFLAGS

mm: separate out FOLIO_FLAGS from PAGEFLAGS

Patch series "PageFlags cleanups".

We have now successfully removed all of the uses of some of the PageFlags
from the kernel, but there's nothing to stop somebody reintroducing them.
By splitting out FOLIO_FLAGS from PAGEFLAGS, we can stop defining the old
flags; and we do that in some of the later patches.

After doing this, I realised that dump_page() was living dangerously; we
could end up calling folio_test_foo() on a pointer which no longer pointed
to a folio (as dump_page() is not necessarily called when the caller has a
reference to the page).  So I fixed that up.

And then I realised that this was the key to making dump_page() take a
const argument, which means we can constify the page flags testing, which
means we can remove more cast-away-the-const bad code.

And here's where I ended up.

This patch (of 8):

We've progressed far enough with the folio transition that some flags are
now no longer checked on pages, but only on folios.  To prevent new users
appearing, prepare to only define the folio versions of the flag
test/set/clear.

Link: https://lkml.kernel.org/r/20240227192337.757313-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20240227192337.757313-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>