mm/sharepool: Use "tgid" instead of "pid" to find a task

ascend inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I612UG


CVE: NA

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To support container scenario, use tgid instead of pid to find a
specific task. In normal cases, "tgid" represent a process in init_pid_ns,
this patch should not introduce problems to existing code.

Rename the input parameter "int pid" to "int tgid" in following
exported interfaces:
1.mg_sp_group_id_by_pid()
2.mg_sp_group_add_task()
3.mg_sp_group_del_task()
4.mg_sp_make_share_k2u()
5.mg_sp_make_share_u2k()
6.mg_sp_config_dvpp_range()

Besides, rename these static function together:
1.__sp_find_spg_locked()
2.__sp_find_spg()

The following function use "current->pid" to find spg, change
"current->pid" to "current->tgid".
1.find_or_alloc_sp_group()
2.sp_alloc_prepare()
3.mg_sp_make_share_k2u()

Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>