mm/page_io: introduce bio_first_folio_all()

Introduce bio_first_folio_all() to return a folio, which makes it easier
to use.

Link: https://lkml.kernel.org/r/20230721034451.16412-4-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/Documentation/block/biovecs.rst b/Documentation/block/biovecs.rst
index ddb867e0..b9dc0c9 100644
--- a/Documentation/block/biovecs.rst
+++ b/Documentation/block/biovecs.rst
@@ -134,6 +134,7 @@
 	bio_for_each_bvec_all()
 	bio_first_bvec_all()
 	bio_first_page_all()
+	bio_first_folio_all()
 	bio_last_bvec_all()
 
 * The following helpers iterate over single-page segment. The passed 'struct