mm: Refactor code in reliable_report_meminfo()

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


CVE: NA

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Now reliable_report_meminfo() will exit if memory reliable is not enabled.

Percpu counter nr_pagecache_pages will be sumed with nr_buddy_pages
together.

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>