drm: sti: convert driver to atomic modeset

v1: This patch does the minimum to make sti driver use atomic helpers.
No big bang, only adapt some functions to new call order.

v2: Use dpms and page flip atomic helpers

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
diff --git a/drivers/gpu/drm/sti/sti_drm_drv.h b/drivers/gpu/drm/sti/sti_drm_drv.h
index ec5e2eb..c413aa3 100644
--- a/drivers/gpu/drm/sti/sti_drm_drv.h
+++ b/drivers/gpu/drm/sti/sti_drm_drv.h
@@ -24,6 +24,12 @@
 	struct sti_compositor *compo;
 	struct drm_property *plane_zorder_property;
 	struct drm_device *drm_dev;
+
+	struct {
+		struct drm_atomic_state *state;
+		struct work_struct work;
+		struct mutex lock;
+	} commit;
 };
 
 #endif