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/sysprop/SurfaceFlingerProperties.sysprop b/services/surfaceflinger/sysprop/SurfaceFlingerProperties.sysprop
index 421484f..4d25a7a 100644
--- a/services/surfaceflinger/sysprop/SurfaceFlingerProperties.sysprop
+++ b/services/surfaceflinger/sysprop/SurfaceFlingerProperties.sysprop
@@ -445,3 +445,12 @@
     access: Readonly
     prop_name: "ro.surface_flinger.update_device_product_info_on_hotplug_reconnect"
 }
+
+# Enables the frame rate override feature
+prop {
+    api_name: "enable_frame_rate_override"
+    type: Boolean
+    scope: Public
+    access: Readonly
+    prop_name: "ro.surface_flinger.enable_frame_rate_override"
+}