page-writeback: convert write_cache_pages() to use filemap_get_folios_tag()

page-writeback: convert write_cache_pages() to use filemap_get_folios_tag()

Convert function to use folios throughout.  This is in preparation for the
removal of find_get_pages_range_tag().  This change removes 8 calls to
compound_head(), and the function now supports large folios.

Link: https://lkml.kernel.org/r/20230104211448.4804-5-vishal.moola@gmail.com
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Matthew Wilcow (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>