share_pool: Implement sp_make_share_k2u()

ascend inclusion
category: Feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4NDAW


CVE: NA

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This share a kernel memory range to userspace.
Introduce vm_struct flag VM_SHAREPOOL to indicate that a vm_struct
shared to userspace and we cannot vfree such a vm_area.

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
Signed-off-by: Zhou Guanghui <zhouguanghui1@huawei.com>
Reviewed-by: Kefeng <Wang&lt;wangkefeng.wang@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>