Revert "cgroup: remove bind() method from cgroup_subsys."

This reverts commit 84cfb6ab484b442d5115eb3baf9db7d74a3ea626.  There
are scheduled changes which make use of the removed callback.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Rami Rosen <ramirose@gmail.com>
Cc: Li Zefan <lizefan@huawei.com>
3 files changed