cgroup: Export cgroup.kill from cgroupv2 to cgroupv1

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4X0YD?from=project-issue


CVE: NA

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Export cgroup.kill feature from cgroupv2 to cgroupv1. Therefore, user
can kill all process in one cgroup and its subcgroups instead of kill them
one by one.

Signed-off-by: Lu Jialin <lujialin4@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>