mm: Show ReliableTaskUsed in /proc/meminfo

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SK3S


CVE: NA

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Add ReliableTaskUsed in /proc/meminfo if memory reliable is enabled.
- ReliableTaskUsed: reliable memory used by special user tasks and
  global init process

Change variable reliable_user_used_nr_page to a more accurate
reliable_task_used_nr_page.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: Kefeng <Wang&lt;wangkefeng.wang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>