mm/page_idle: Convert page_idle_clear_pte_refs() to use a folio

The PG_idle and PG_young bits are ignored if they're set on tail
pages, so ensure we're passing a folio around.

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