shmem: Count and show reliable shmem info

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


CVE: NA

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Count reliable shmem usage based on NR_SHMEM.
Add ReliableShmem in /proc/meminfo to show reliable memory info
used by shmem.

- ReliableShmem: reliable memory used by shmem

Signed-off-by: Zhou Guanghui <zhouguanghui1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>