Add rules for system_update service.

system_update service manages system update information: system updater
(priv_app) publishes the pending system update info through the service,
while other apps can read the info accordingly (design doc in
go/pi-ota-platform-api).

This CL adds the service type, and grants priv_app to access the service.

Bug: 67437079
Test: Build and flash marlin image. The system_update service works.
Change-Id: I7a3eaee3ecd3e2e16b410413e917ec603566b375
diff --git a/private/priv_app.te b/private/priv_app.te
index ec52d56..e3eec83 100644
--- a/private/priv_app.te
+++ b/private/priv_app.te
@@ -96,6 +96,10 @@
 binder_call(priv_app, storaged)
 allow priv_app storaged_service:service_manager find;
 
+# Allow GMS core to access system_update_service (e.g. to publish pending
+# system update info).
+allow priv_app system_update_service:service_manager find;
+
 # Allow GMS core to communicate with statsd.
 binder_call(priv_app, statsd)