dm: virtio-blk: add multiple queues (mq) support

Virtio-blk can support multiple virtqueues (mq) which is negotiated
between FE and BE by the feature bit VIRTIO_BLK_F_MQ. The virtqueue
number of virtio-blk can be specified by "mq=x" in the parameter.
For example: "virtio-blk,iothread,mq=2,..."

Tracked-On: #8612

Signed-off-by: Jian Jun Chen <jian.jun.chen@intel.com>
Acked-by: Wang, Yu1 <yu1.wang@intel.com>

devicemodel/core/main.c

@@ -233,6 +233,12 @@ virtio_uses_msix(void)
 	return virtio_msix;
 }
 
+int
+guest_cpu_num(void)
+{
+	return guest_ncpus;
+}
+
 size_t
 high_bios_size(void)
 {