mm/sharepool: Check sp_is_enabled() in all exported interfaces

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5DS9S


CVE: NA

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We should forbid the usage of sharepool interfaces if sharepool is not
enabled. Or undefined behaviour would panic the kernel.

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>