arm64: add new config CONFIG_PMU_WATCHDOG

hulk inclusion
category: bugfix
bugzilla: 13794
CVE: NA

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Add new config CONFIG_PMU_WATCHDOG for watchdog implementation method
configuration.

Signed-off-by: Wei Li <liwei391@huawei.com>
Reviewed-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>