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
Change-Id: Ida0e13f9a7c420f5f363d1feeacf882d8b76a8fa
Test: atest FrameRateOverrideHostTest
diff --git a/private/property_contexts b/private/property_contexts
index 6787087..7b6242e 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -983,6 +983,7 @@
 ro.surface_flinger.color_space_agnostic_dataspace         u:object_r:surfaceflinger_prop:s0 exact int
 ro.surface_flinger.refresh_rate_switching                 u:object_r:surfaceflinger_prop:s0 exact bool
 ro.surface_flinger.update_device_product_info_on_hotplug_reconnect u:object_r:surfaceflinger_prop:s0 exact bool
+ro.surface_flinger.enable_frame_rate_override             u:object_r:surfaceflinger_prop:s0 exact bool
 
 ro.sf.disable_triple_buffer u:object_r:surfaceflinger_prop:s0 exact bool
 ro.sf.lcd_density           u:object_r:surfaceflinger_prop:s0 exact int