tools/virtio: add dma stubs

Fixes build after recent IOMMU-related changes,
mustly by adding more stubs.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tools/virtio/linux/virtio.h

@@ -3,8 +3,12 @@
 #include <linux/scatterlist.h>
 #include <linux/kernel.h>
 
+struct device {
+	void *parent;
+};
+
 struct virtio_device {
-	void *dev;
+	struct device dev;
 	u64 features;
 };