libprocessgroup: adopt cgroup v2 freezer search path am: a7148f82a1 am: 3067ef3ec0

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1585102

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I0e947e6d0fa01a87f6a71e56cd2f9be1fc06f2fa