dhugetlb: introduce page_belong_to_dynamic_hugetlb() function

hulk inclusion
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I8YWPT


CVE: NA

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Use page_belong_to_dynamic_hugetlb() helper to check whether a page is
from dynamic hugetlb pool.

No functional change.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>