share_pool: Reserve the va space for share_pool

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


CVE: NA

-------------------

Change the mmap_base in mm_struct and check the limit in
get_unmapped_area.

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Signed-off-by: Peng Wu <wupeng58@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>