block: use an xarray for disk->part_tbl

Now that no fast path lookups in the partition table are left, there is
no point in micro-optimizing the data structure for it.  Just use a bog
standard xarray.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 43990b1..4c97434 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -865,7 +865,7 @@ void blk_queue_set_zoned(struct gendisk *disk, enum blk_zoned_model model)
 		 * we do nothing special as far as the block layer is concerned.
 		 */
 		if (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) ||
-		    disk_has_partitions(disk))
+		    !xa_empty(&disk->part_tbl))
 			model = BLK_ZONED_NONE;
 		break;
 	case BLK_ZONED_NONE: