Add a sysprop to control layer caching

Adding 'ro.surface_flinger.enable_layer_caching' to control
whether layer caching feature should be enabled or not.

Bug: 158790260
Change-Id: I3ceb84d2a9209b2c422ba93057e9323ca6816ca5
diff --git a/private/property_contexts b/private/property_contexts
index 25e9d87..dc4335f 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -990,6 +990,7 @@
 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.surface_flinger.enable_layer_caching                   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