drm_hwcomposer: implement squashing

Change-Id: Ifd4feaa0de303ddfd519d4415ab31d2a72f26022
diff --git a/drmcomposition.h b/drmcomposition.h
index ed176f1..80a7eea 100644
--- a/drmcomposition.h
+++ b/drmcomposition.h
@@ -34,6 +34,7 @@
 
 struct DrmCompositionDisplayLayersMap {
   int display;
+  bool geometry_changed = true;
   std::vector<DrmHwcLayer> layers;
 
   DrmCompositionDisplayLayersMap() = default;