mm: Reserve field in mm_struct for memory reliable

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


DTS: #896
CVE: NA

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Reserved a variable in mm_struct while will be used by memory reliable.

Signed-off-by: Peng Wu <wupeng58@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>