drm/virtio: add create_handle support.

Add create_handle support to virtio fb. Without this, screenshot tool
in chromium OS can't work.
Signed-off-by: Lepton Wu <ytht.net@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20171108184209.46211-1-ytht.net@gmail.comSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_display.c

@@ -71,7 +71,19 @@ virtio_gpu_framebuffer_surface_dirty(struct drm_framebuffer *fb,
 	return virtio_gpu_surface_dirty(virtio_gpu_fb, clips, num_clips);
 }
 
+static int
+virtio_gpu_framebuffer_create_handle(struct drm_framebuffer *fb,
+				     struct drm_file *file_priv,
+				     unsigned int *handle)
+{
+	struct virtio_gpu_framebuffer *virtio_gpu_fb =
+		to_virtio_gpu_framebuffer(fb);
+
+	return drm_gem_handle_create(file_priv, virtio_gpu_fb->obj, handle);
+}
+
 static const struct drm_framebuffer_funcs virtio_gpu_fb_funcs = {
+	.create_handle = virtio_gpu_framebuffer_create_handle,
 	.destroy = virtio_gpu_user_framebuffer_destroy,
 	.dirty = virtio_gpu_framebuffer_surface_dirty,
 };