mm/dynamic_pool: fill dpool with HugeTLB 1G pages

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8S9BY


CVE: NA

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This patch imlements the function of filling dpool with HugeTLB 1G pages.
The user should prepare <number> of 1G HugeTLB pages on node of <nid> and
then input the command in the corresponding memcg:
	`echo <nid> <number> > dhugetlb.nr_pages`

The pages is coming from HugeTLB 1G free pages and will be returned to
HugeTLB when destroy the dpool.

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