Allow blank_screen to make binder calls to the servicemanager

blank_screen can not find and use the lights HAL if it cannot use the servicemanager. This
broke turning off the display during shutdown.

Change-Id: I6aff1cb71f805637abc79493ba2574143c5cf7cf
Test: adb root; adb shell setenforce 1; adb shell setprop ctl.start blank_screen
Test: adb logcat -b all | grep 'denied'
Bug: 151363454
diff --git a/public/hal_light.te b/public/hal_light.te
index 1e70b74..4aa824a 100644
--- a/public/hal_light.te
+++ b/public/hal_light.te
@@ -4,10 +4,13 @@
 
 hal_attribute_hwservice(hal_light, hal_light_hwservice)
 
+# server adds itself via service_manager
 add_service(hal_light_server, hal_light_service)
 binder_call(hal_light_server, servicemanager)
 
+# client finds and uses server via service_manager
 allow hal_light_client hal_light_service:service_manager find;
+binder_use(hal_light_client)
 
 allow hal_light_server dumpstate:fifo_file write;