vmscan: convert lazy freeing to folios

Remove a hidden call to compound_head(), and account nr_pages instead of a
single page.  This matches the code in lru_lazyfree_fn() that accounts
nr_pages to PGLAZYFREE.

Link: https://lkml.kernel.org/r/20220504182857.4013401-12-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>