block: add queue_is_mq() helper

Various spots check for q->mq_ops being non-NULL, but provide
a helper to do this instead.

Where the ->mq_ops != NULL check is redundant, remove it.

Since mq == rq-based now that legacy is gone, get rid of the
queue_is_rq_based() and just use queue_is_mq() everywhere.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 13ba201..e9c332b 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -421,7 +421,7 @@ int blk_revalidate_disk_zones(struct gendisk *disk)
 	 * BIO based queues do not use a scheduler so only q->nr_zones
 	 * needs to be updated so that the sysfs exposed value is correct.
 	 */
-	if (!queue_is_rq_based(q)) {
+	if (!queue_is_mq(q)) {
 		q->nr_zones = nr_zones;
 		return 0;
 	}