cgroup/cpuset: Expose cpuset filesystem with cpuset v1 only

The cpuset filesystem is a legacy interface to cpuset controller with
(pre-)v1 features. It makes little sense to co-mount it on systems
without cpuset v1, so do not build it when cpuset v1 is not built
neither.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>