cgroup: add provision to move task to root cgroup

In some cases we may need to a move task out its cgroup to avoid
priority inversion, when it is holding critical resources
required by other higher priority tasks. So add a mechanism to
move a task out of its cgroup to avoid the task being starved.

CRs-Fixed: 983539
Change-Id: I167d7f965d133ec996bd13f57183468e8399bacc
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>