As part of the MatthewWilcox/Memdescs project, we will be getting rid of page flags.

The flags word in struct page contains such things as node/zone/section.  These will continue to be in the high bits of the newly created memdesc_flags_t.  The low bits of memdesc_flags_t will contain some of the existing page flags, but others will be handled differently.

The slab flags are already split out and will not be discussed here.

For folios,
 * PG_locked will be FL_locked
 * PG_writeback will be FL_writeback
 * PG_referenced will be FL_referenced
 * PG_uptodate will be FL_uptodate
 * PG_dirty will be FL_dirty
 * PG_lru will be FL_lru
 * PG_head will no longer exist
 * PG_waiters will be FL_waiters
 * PG_active will be FL_active
 * PG_workingset will be FL_workingset
 * PG_owner_priv_1 will be FL_owner_1
 * PG_owner_2 will be FL_owner_2
 * PG_arch_1 will be FL_arch_1
 * PG_reserved will be a memdesc type
 * PG_private will be replaced with checks of folio->private
 * PG_private_2 will disappear, possibly before folio and page are split
 * PG_reclaim will be FL_reclaim
 * PG_swapbacked will be FL_swapbacked
 * PG_unevictable will be FL_unevictable
 * PG_dropbehind will be FL_dropbehind
 * PG_mlocked will be FL_mlocked
 * PG_hwpoison will be a memdesc type
 * PG_young will be FL_young
 * PG_idle will be FL_idle