Allow system_server to set audio properties

Defined a new signal intended to allow the system to reboot
the audio/soundtrigger HAL process.

Fixes: 153461865
Test: See main change in topic
Change-Id: I1e4a770670bb1274fa6a23cd0641f2554d4679f7
Merged-In: I1e4a770670bb1274fa6a23cd0641f2554d4679f7
diff --git a/private/property_contexts b/private/property_contexts
index cf44144..051dd8c 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -22,6 +22,7 @@
 hw.                     u:object_r:system_prop:s0
 ro.hw.                  u:object_r:system_prop:s0
 sys.                    u:object_r:system_prop:s0
+sys.audio.              u:object_r:audio_prop:s0
 sys.init.perf_lsm_hooks u:object_r:init_perf_lsm_hooks_prop:s0
 sys.cppreopt            u:object_r:cppreopt_prop:s0
 sys.lpdumpd             u:object_r:lpdumpd_prop:s0