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 <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Gerd Hoffmann <[e-mail]>

drivers/gpu/drm/virtio/virtgpu_display.c

···
 	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,
 };