mm: sharepool: use built-in-statistics

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5J0YW


CVE: NA
--------------------------------

Sharepool owns an statistics system which allow user to check the memory
use easily. The statistics codes are quite independent from the major
functions. However, the realization is very similar with the major
functions, which doubles the lock use and cause nesting problems.

Thus we remove the statistics system, and put all the statistics into raw
data structures as built-in statistics. The user api did not change.
This can greatly reduce the complexity of locks, as well as remove hundred
lines of redundant codes.

Signed-off-by: Guo Mengqi <guomengqi3@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>