grant mediadrmserver permission to read dir from /system/*

hal_client_domain no longer allows read dir permission, in order
to load .so from /system/lib, we have to add this permission ourselves.

bug: 37476803
Change-Id: I1711d158c2f4580f50ac244da10c489df003cc18
diff --git a/public/mediadrmserver.te b/public/mediadrmserver.te
index eccefc6..cef8121 100644
--- a/public/mediadrmserver.te
+++ b/public/mediadrmserver.te
@@ -16,6 +16,7 @@
 allow mediadrmserver mediametrics_service:service_manager find;
 allow mediadrmserver processinfo_service:service_manager find;
 allow mediadrmserver surfaceflinger_service:service_manager find;
+allow mediadrmserver system_file:dir r_dir_perms;
 
 add_service(mediadrmserver, mediacasserver_service)