sepolicy: rules for uid/pid cgroups v2 hierarchy

Bug: 168907513
Test: verified the correct working of the v2 uid/pid hierarchy in normal
and recovery modes

This reverts commit aa8bb3a29b92a342c42c802edac269da5984d1df.

Change-Id: Ib344d500ea49b86e862e223ab58a16601eebef47
diff --git a/private/system_app.te b/private/system_app.te
index 0aa46e3..36208bf 100644
--- a/private/system_app.te
+++ b/private/system_app.te
@@ -158,6 +158,7 @@
 
 # Settings app writes to /dev/stune/foreground/tasks.
 allow system_app cgroup:file w_file_perms;
+allow system_app cgroup_v2:file w_file_perms;
 
 control_logd(system_app)
 read_runtime_log_tags(system_app)