SurfaceFlinger: add a sysprop to control frame rate override

Adding 'ro.surface_flinger.enable_frame_rate_override' to control
whether frame rate override feature should be enabled or not.

Bug: 170502573
Bug: 176940141
Test: atest FrameRateOverrideHostTest
Change-Id: Id7b7a405c6493606af4149d77a4c3d90afc9a5b7
diff --git a/services/surfaceflinger/SurfaceFlingerProperties.cpp b/services/surfaceflinger/SurfaceFlingerProperties.cpp
index 97725ec..c043866 100644
--- a/services/surfaceflinger/SurfaceFlingerProperties.cpp
+++ b/services/surfaceflinger/SurfaceFlingerProperties.cpp
@@ -376,5 +376,9 @@
             defaultValue);
 }
 
+bool enable_frame_rate_override(bool defaultValue) {
+    return SurfaceFlingerProperties::enable_frame_rate_override().value_or(defaultValue);
+}
+
 } // namespace sysprop
 } // namespace android