docs: cgroup-v1: wrap remaining admonitions in admonition blocks

Wrap two other admonitions in appropriate blocks in order for readers to
pay more attention to block contents:

  * hint:: for editor's note
  * warning:: for move charges deprecation

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>