sepolicy: Give access to ahal to flinger standby prop

Allow Vendor Audio HAL to update Audio Flinger standby
idle timeout.

Bug: 181967247
Change-Id: I7ae992bde5fdcf81ce2ca7a5a93e5e70aab1b56c
diff --git a/private/property_contexts b/private/property_contexts
index 306b40a..28c93ed 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -300,8 +300,9 @@
 # history size.
 ro.lib_gui.frame_event_history_size u:object_r:bq_config_prop:s0
 
-af.fast_track_multiplier     u:object_r:audio_config_prop:s0 exact int
-ro.af.client_heap_size_kbyte u:object_r:audio_config_prop:s0 exact int
+af.fast_track_multiplier         u:object_r:audio_config_prop:s0 exact int
+ro.af.client_heap_size_kbyte     u:object_r:audio_config_prop:s0 exact int
+ro.audio.flinger_standbytime_ms  u:object_r:audio_config_prop:s0 exact int
 
 audio.camerasound.force         u:object_r:audio_config_prop:s0 exact bool
 audio.deep_buffer.media         u:object_r:audio_config_prop:s0 exact bool