mm: convert free_unref_page_list() to use folios

Most of its callees are not yet ready to accept a folio, but we know all
of the pages passed in are actually folios because they're linked through
->lru.

Link: https://lkml.kernel.org/r/20240227174254.710559-3-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>