UPSTREAM: cgroup add cftype->open/release() callbacks

Pipe the newly added kernfs->open/release() callbacks through cftype.
While at it, as cleanup operations now can be performed from
->release() instead of ->seq_stop(), make the latter optional.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Acked-by: Zefan Li <lizefan@huawei.com>

(cherry picked from commit e90cbebc3fa5caea4c8bfeb0d0157a0cee53efc7)

Bug: 111308141
Test: modified lmkd to use PSI and tested using lmkd_unit_test

Change-Id: Iff9794cbbc2c7067c24cb2f767bbdeffa26b5180
Signed-off-by: Suren Baghdasaryan <surenb@google.com>