mm/pin_mem: refactor pin memory mem reserve and pid reserve code

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4REE5


CVE: NA

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1.Refactor pin memory mem reserve:
Move the memory reserve functions to pin_mem.c,
and avoid using unnecessary macros.

2.Refactor pid reserve code:
In oder to avoid using unnecessary compile macros in pid.c,
add stub functions for free_reserved_pid and reserve_pids.

Signed-off-by: Jingxian He <hejingxian@huawei.com>
Reviewed-by: Kefeng <Wang&lt;wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>