hulk inclusion
category: performance
bugzilla: 187468, https://gitee.com/openeuler/kernel/issues/I61HSG

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The zswap initialization consumes some memory. If we don't use zswap,
there's no need to initial it. So delay the initializaton of zswap until
the first enablement.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>