mm/writeback: Convert tracing writeback_page_template to folios

Rename writeback_dirty_page() to writeback_dirty_folio() and
wait_on_page_writeback() to folio_wait_writeback().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>