mm/sharepool: Rename sp_group operations

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I650K6



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Rename sp_group_drop[_locked] to sp_group_put[_locked].
Rename __sp_find_spg[_locked] to sp_group_get[_locked].

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>