sepolicy: restrict access to uid_cpupower files

Do not let apps read /proc/uid_cpupower/time_in_state,
/proc/uid_cpupower/concurrent_active_time,
/proc/uid_cpupower/concurrent_policy_time.

b/71718257

Test: Check that they can't be read from the shell
    without root permissions and system_server was able
    to read them

Change-Id: I812694adfbb4630f7b56aa7096dc2e6dfb148b15
diff --git a/private/system_server.te b/private/system_server.te
index 6ebcab5..642c8bd 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -718,6 +718,7 @@
 }:file r_file_perms;
 
 allow system_server proc_uid_time_in_state:dir r_dir_perms;
+allow system_server proc_uid_cpupower:file r_file_perms;
 
 r_dir_file(system_server, rootfs)