net: hns: add attribute cpld_ctrl for dsaf port node

This patch adds attribute cpld_ctrl for dsaf port node, parses the syscon
for mac_cb from dts, and changes the method of access the cpld related
registers through syscon.

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>