drm: use page flip event to signal flip completion

We don't actually know which frame number the flip will complete on, so
userspace needs a specific flip notification to tell it when the last flip
completed.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Kristian Høgsberg <krh@bitplanet.net>
diff --git a/include/drm/drm.h b/include/drm/drm.h
index 3919a4f..309d0a5 100644
--- a/include/drm/drm.h
+++ b/include/drm/drm.h
@@ -718,6 +718,7 @@
 };
 
 #define DRM_EVENT_VBLANK 0x01
+#define DRM_EVENT_FLIP_COMPLETE 0x02
 
 struct drm_event_vblank {
 	struct drm_event base;