mm/dynamic_pool: support to flow pages between 1G and 2M pages pool

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


CVE: NA

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Support to demote pages in 1G pages pool to 2M size.
Support to promote pages in 2M pages pool to 1G size.

The demotion is occurred when small order pages is not enough, and the
promotion is occurred when destroy the dpool.

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