hugetlbfs: Add config to isolate the code of share_pool

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6HRGK



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Add config to encapsulate the code introduced in
2fb141bf9c23 ("[Huawei] mm: sharepool: fix hugepage_rsvd count increase
error").

Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>