mm: convert page type macros to enum

Changing PG_slab from a page flag to a page type in commit 46df8e73
("mm: free up PG_slab") in has the unintended consequence of removing the
PG_slab constant from kernel debuginfo.  The commit does add the value to
the vmcoreinfo note, which allows debuggers to find the value without
hardcoding it.  However it's most flexible to continue representing the
constant with an enum.  To that end, convert the page type fields into an
enum.  Debuggers will now be able to detect that PG_slab's type has
changed from enum pageflags to enum pagetype.

Link: https://lkml.kernel.org/r/20240607202954.1198180-1-stephen.s.brennan@oracle.com


Fixes: 46df8e73 ("mm: free up PG_slab")
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hao Ge <gehao@kylinos.cn>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Omar Sandoval <osandov@osandov.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>