PSI: Introduce avgs and total calculation for cgroup reclaim

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8BCV4



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Introduce avgs and total calculation depend on the fine grained time
collect in psi_avgs_works() for cgroup_reclaim. The results will be
shown in pressure.stat, which will be done in the next patch.

Signed-off-by: Lu Jialin <lujialin4@huawei.com>