share_pool: Rename sp_spg_stat to sp_overall_stat

ascend inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4EUVI


CVE: NA

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We are going to redesign the accounting subsystem of share pool.
First we need to disambiguate the meaning of sp_spg_stat, as it is
system-level not spg-level.

Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
Reviewed-by: Ding Tianhong <dingtianhong@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>