Wrap cgroup writeback v1 logic to prevent build errors without
CONFIG_CGROUPS or CONFIG_CGROUP_WRITEBACK.
Reported-by: Nkbuild test robot <lkp@intel.com>
Cc: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>