mm/dynamic_hugetlb: add split page function

hulk inclusion
category: feature
bugzilla: 46904, https://gitee.com/openeuler/kernel/issues/I4QSHG


CVE: NA

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Currently, dynamic hugetlb support 1G/2M/4K pages. In the beginning,
there were only 1G pages in the hpool. Add function to split pages
in dhugetlb_pool. If 4K pages are insufficient, try to split 2M pages,
and if 2M pages are insufficient, try to split 1G pages.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>