etmem: add etmem swap feature

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8T1MB?from=project-issue


CVE: NA

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This patch implements the etmem swap feature.

etmem swap, like etmem scan, also communicated with the user space program
thought a registered proc file system. It adds target pages to swap cache
to be further reclaimed by kswapd, and dwell in swap space.

Signed-off-by: yanxiaodan <yanxiaodan@huawei.com>
Signed-off-by: linmiaohe <linmiaohe@huawei.com>
Signed-off-by: louhongxiang <louhongxiang@huawei.com>
Signed-off-by: liubo <liubo254@huawei.com>
Signed-off-by: geruijun <geruijun@huawei.com>
Signed-off-by: Yuchen Tang <tangyuchen5@huawei.com>