CachedAppOptimizer: enable single cgroup freezer

The cgroup v2 uid/pid hierarchy was reverted because of
http://b/179006802 leaving the underlying freezer implementation to a
single cgroup. Enable the freezer at boot until the new hierarchy can be
brought back.

Bug: 179006802
Test: verified that the freezer is enabled at boot
Change-Id: I88041a3efb06724e4bc2d78fea017778c365d387

services/core/java/com/android/server/am/CachedAppOptimizer.java

@@ -556,6 +556,10 @@ public final class CachedAppOptimizer {
 
             if (state == '1' || state == '0') {
                 supported = true;
+                // This is a workaround after reverting the cgroup v2 uid/pid hierarchy due to
+                // http://b/179006802.
+                // TODO: remove once the uid/pid hierarchy is restored
+                enableFreezerInternal(true);
             } else {
                 Slog.e(TAG_AM, "unexpected value in cgroup.freeze");
             }