drm_hwcomposer: Add rotation support for hw planes

This patch adds support for transformed layers by using the
rotation property on drm planes.

Bug: chrome-os-partner:42093
Test: On smaug using
	adb shell content insert --uri content://settings/system --bind name:s:user_rotation --bind value:i:<R>

Change-Id: I86bb8ef2f77b5d046a5fddd57db4b87070b5801f
Signed-off-by: Sean Paul <seanpaul@chromium.org>
diff --git a/drmplane.h b/drmplane.h
index 96cd85c..1969d52 100644
--- a/drmplane.h
+++ b/drmplane.h
@@ -51,6 +51,7 @@
   const DrmProperty &src_y_property() const;
   const DrmProperty &src_w_property() const;
   const DrmProperty &src_h_property() const;
+  const DrmProperty &rotation_property() const;
 
  private:
   DrmPlane(const DrmPlane &);
@@ -72,6 +73,7 @@
   DrmProperty src_y_property_;
   DrmProperty src_w_property_;
   DrmProperty src_h_property_;
+  DrmProperty rotation_property_;
 };
 }