blk-mq: provide a default queue mapping for virtio device

Similar to the PCI version, just calling into virtio instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/block/Kconfig b/block/Kconfig
index 8bf114a..3523b4f 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -165,4 +165,9 @@
 	depends on BLOCK && PCI
 	default y
 
+config BLK_MQ_VIRTIO
+	bool
+	depends on BLOCK && VIRTIO
+	default y
+
 source block/Kconfig.iosched