hw/display/virtio-gpu: Put the virtio-gpu-device into the display category

The virtio-gpu-pci device is already in the display category, so the
virtio-gpu-device should be there, too.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/display/virtio-gpu.c

@@ -1321,6 +1321,7 @@ static void virtio_gpu_class_init(ObjectClass *klass, void *data)
 
     vdc->reset = virtio_gpu_reset;
 
+    set_bit(DEVICE_CATEGORY_DISPLAY, dc->categories);
     dc->props = virtio_gpu_properties;
     dc->vmsd = &vmstate_virtio_gpu;
     dc->hotpluggable = false;