firmware: arm_sdei: add interrupt binding api

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

----------------------------------------

This patch add a interrupt binding api function which returns the binded
event number.

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