UPSTREAM: kernfs: add kernfs_ops->open/release() callbacks

Add ->open/release() methods to kernfs_ops.  ->open() is called when
the file is opened and ->release() when the file is either released or
severed.  These callbacks can be used, for example, to manage
persistent caching objects over multiple seq_file iterations.

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

(cherry picked from commit 0e67db2f9fe91937e798e3d7d22c50a8438187e1)

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

Change-Id: Id06e9d5c6da1280bcdd4dc86309dcfaf52b8f9a4
Signed-off-by: Suren Baghdasaryan <surenb@google.com>