cgroup: rename Documentation/cgroups/ to Documentation/cgroup-legacy/

In preparation for adding cgroup2 documentation, rename
Documentation/cgroups/ to Documentation/cgroup-legacy/.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
(cherry picked from commit 0d942766453f3d23a51e0a2d430340a178b0903e)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
14 files changed