firmware: arm_sdei: make 'sdei_api_event_disable/enable' public

euler inclusion
category: feature
Bugzilla: 5515
CVE: N/A

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NMI Watchdog need to enable the event for each core individually. But the
existing public api 'sdei_event_enable' enable events for all cores when
the event type is private.

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>