RDMA/hns: Add cmd for clear extend doorbell list

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

When unloading the RoCE driver, the address of
DB was reserved in hw, which should be clear
when reloading the RoCE driver.

Feature or Bugfix: Bugfix

Signed-off-by: wangsirong <wangsirong@huawei.com>
Signed-off-by: liyangyang (M) <liyangyang20@huawei.com>
Reviewed-by: oulijun <oulijun@huawei.com>
Reviewed-by: liuyixian <liuyixian@huawei.com>
Reviewed-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>