mm: Convert find_lock_entries() to use a folio_batch

find_lock_entries() already only returned the head page of folios, so
convert it to return a folio_batch instead of a pagevec.  That cascades
through converting truncate_inode_pages_range() to
delete_from_page_cache_batch() and page_cache_delete_batch().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>