block: Move blk_mq_bio_list_merge() into blk-merge.c

Move the blk_mq_bio_list_merge() into blk-merge.c and
rename it as a generic name.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk.h b/block/blk.h
index 49e2928..d6152d2 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -177,6 +177,8 @@ bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
 		struct bio *bio);
 bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		unsigned int nr_segs, struct request **same_queue_rq);
+bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
+			struct bio *bio, unsigned int nr_segs);
 
 void blk_account_io_start(struct request *req);
 void blk_account_io_done(struct request *req, u64 now);