ext2: Convert ext2_check_page to ext2_check_folio

Support in this function for large folios is limited to supporting
filesystems with block size > PAGE_SIZE.  This new functionality will only
be supported on machines without HIGHMEM, so the problem of kmap_local
only being able to map a single page in the folio can be ignored.
We will not use large folios for ext2 directories on HIGHMEM machines.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230921200746.3303942-2-willy@infradead.org>