mm: constify testing page/folio flags

Now that dump_page() takes a const argument, we can constify all the page
flag tests.

Link: https://lkml.kernel.org/r/20240227192337.757313-7-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>