Add ITradeInMode service sepolicy.

This defines a new service for the ITradeInMode, and grants it (through
system_server) permissions to modify persist.adb.tradeinmode.

Bug: 307713521
Test: manual test
Change-Id: I0afb349863aaf8488dd3dabaf8e7319e297bffaf
diff --git a/private/platform_app.te b/private/platform_app.te
index 320624c..e60dcdd 100644
--- a/private/platform_app.te
+++ b/private/platform_app.te
@@ -99,6 +99,7 @@
 allow platform_app system_api_service:service_manager find;
 allow platform_app vr_manager_service:service_manager find;
 allow platform_app stats_service:service_manager find;
+allow platform_app tradeinmode_service:service_manager find;
 
 # Allow platform apps to log via statsd.
 binder_call(platform_app, statsd)