sdei_watchdog: do not disable sdei_watchdog event when failed to initialise SDEI

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

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When we modify '/proc/sys/kernel/watchdog_thresh', kernel will call
'watchdog_nmi_disable' before change 'watchdog_thresh'. If firmware does
not support SDEI, we will get 'SDEI NMI Watchdog: Disable NMI Watchdog
failed on cpuX'. It is because we failed to disable sdei_watchdog event.
It has no bad effect.

This patch add a flag to record whether we have registered sdei_watchdog
successfully and do not disable sdei_watchdog event if we failed to
register sdei_watchdog event.

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>