vmscan: convert the activate_locked portion of shrink_page_list to folios

This accounts the number of pages activated correctly for large folios.

Link: https://lkml.kernel.org/r/20220504182857.4013401-14-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>