drm_hwcomposer: Add getter/setter for content_type

Optionally, get the content_type drm property. Add implementation to
HwcDisplay::SetContentType to set this property.

Change-Id: I910e064876d13205abc7caaac342daaff8f38599
Signed-off-by: Sasha McIntosh <sashamcintosh@google.com>
diff --git a/hwc2_device/HwcDisplay.h b/hwc2_device/HwcDisplay.h
index 87d2da7..be97623 100644
--- a/hwc2_device/HwcDisplay.h
+++ b/hwc2_device/HwcDisplay.h
@@ -233,6 +233,7 @@
   static constexpr int kCtmCols = 3;
   std::shared_ptr<drm_color_ctm> color_matrix_;
   android_color_transform_t color_transform_hint_{};
+  int32_t content_type_{};
 
   std::shared_ptr<DrmKmsPlan> current_plan_;