virtio-gpu: add atomic_commit function

Do modesets first, then call drm_atomic_helper_commit_planes with
active_only = true.  That way the outputs doesn't get disabled
temporarly on atomic commits.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
index 0a54f43..ecd1c43 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -33,6 +33,7 @@
 
 #include <drm/drmP.h>
 #include <drm/drm_gem.h>
+#include <drm/drm_atomic.h>
 #include <drm/drm_crtc_helper.h>
 #include <ttm/ttm_bo_api.h>
 #include <ttm/ttm_bo_driver.h>