virtio-blk: Allow extended partitions

This will allow up to DISK_MAX_PARTS (256) partitions, with for example
GPT in the guest. Otherwise, the partition scan code will only discover
the first 15 partitions.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/block/virtio_blk.c

@@ -656,6 +656,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 	vblk->disk->private_data = vblk;
 	vblk->disk->fops = &virtblk_fops;
 	vblk->disk->driverfs_dev = &vdev->dev;
+	vblk->disk->flags |= GENHD_FL_EXT_DEVT;
 	vblk->index = index;
 
 	/* configure queue flush support */