block: enable polling by default if a poll map is initalized

If the user did setup polling in the driver we should not require
another know in the block layer to enable it.
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -2826,6 +2826,8 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	q->tag_set = set;
 
 	q->queue_flags |= QUEUE_FLAG_MQ_DEFAULT;
+	if (set->nr_maps > HCTX_TYPE_POLL)
+		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
 
 	if (!(set->flags & BLK_MQ_F_SG_MERGE))
 		blk_queue_flag_set(QUEUE_FLAG_NO_SG_MERGE, q);