mm: Export symbol walk_page_range

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8T1MB?from=project-issue


CVE: NA

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Export symbol walk_page_range, so that etmem_scan can exploit
this for page table walk.

In etmem scan module, it will scan vma segments passed by user
space, and perform page table walk to check the Access bit of
each page, before reporting the scanning results to user space.

Signed-off-by: Yuchen Tang <tangyuchen5@huawei.com>