DO NOT MERGE: Revert "Revert "libcutils: Move sched_policy functions into libprocessgroup""

This reverts commit b5394db6.

Reason for revert: AOSP is fixed with new vendor image

Change-Id: Ie1a2e0200600214a65f4fe2250c903c8e8ce0a29
Signed-off-by: Suren Baghdasaryan <surenb@google.com>