mm/sharepool: Implement mg_sp_group_id_by_pid()

ascend inclusion
category: Feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8LNGH



---------------------------------------------

This is used to find the group for a task.
Also add spg management code.

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>