Revert "libprocessgroup: Remove ACgroupController_getMaxActivati..."

Revert submission 3212512

Reason for revert: Droidmonitor created revert due to b/372273614. Will be verifying through ABTD before submission.

Reverted changes: /q/submissionid:3212512

Change-Id: I0964d1300791334cdc9e98220324d934f7ba113e