mm: enhance variables check and sync for pin mem

hulk inclusion
category: feature
bugzilla: 48159
CVE: N/A

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Enhance variables check and sync for pin mem as followings:
1) Remove unused variable in set_fork_pid;
2) Remove unused calling of access_ok, which is
   called in copy_from_user;
3) Enhance page_map_entry_start check in pin_mem_area;
4) Keep get_page_map_info and create_page_map_info for
   internal use, and increase get_page_map_info_by_pid
   and create_page_map_info_by_pid for external use,
   which is protected by spinlock;
5) Use spin_lock_irqsave instead of spin_lock.

Signed-off-by: Jingxian He <hejingxian@huawei.com>
Reviewed-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>