sh: remove use of PG_arch_1 on individual pages

sh: remove use of PG_arch_1 on individual pages

Patch series "Various page->flags cleanups".

The first two patches are bug fixes, although I'm not sure that either
architecture will have noticed.  There aren't a lot of uses of page->flags
left!  The big build-up here is to reworking stable_page_flags(), which
will definitely be a user-visible change.  I think a welcome one, given
the special case we had to spread the Slab flag into all tail pages.

This patch (of 10):

Since switching to the new page table range API, we do not set the
PG_arch_1 (aka dcache clean) flag on tail pages, only on the folio.  Test
it on the folio.  Also use page_mapped() instead of page_mapcount() as it
is more efficient.

[akpm@linux-foundation.org: fix folio_flags call]
Link: https://lkml.kernel.org/r/20240326171045.410737-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20240326171045.410737-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>