arm64: kfence: scale sample_interval to control re-enabling

hulk inclusion
category: feature
bugzilla: 187071, https://gitee.com/openeuler/kernel/issues/I5DLA7



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KFENCE requires linear map to be mapped at page granularity, this
must done in very early time. To save memory of page table, arm64
only map the pages in KFENCE pool itself at page granularity. Thus,
the kfence pool could not allocated by buddy system.

For the flexibility of KFENCE, scale sample_interval to control whether
support to enable kfence after system startup(re-enabling).
Once sample_interval is set to -1 on arm64, memory for kfence pool
will be allocated from early memory no matter KFENCE is enabled or
not.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>