mm: swap_slots: add per-type slot cache

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7CGGT


CVE: NA

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Since we support per-memcg swapfile control, we need per-type slot
cache to optimize performance. To reduce memory waste, allocate per-type
slot cache when enable feature or online the corresponding swap device.

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