net: hns: add a new dsaf mode for debug port

This patch adds a new dsaf mode named "single-port" mode for debug port.
This mode only contains one debug port. This patch also changes the
method of distinguishing the port type.

Signed-off-by: Daode Huang <huangdaode@hisilicon.com>
Signed-off-by: Yisen Zhuang <yisen.zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>