net: hns3: support of dump mac id and loopback status in debugfs

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

The MAC id and loopback status information are obtained from
the hardware, which will be helpful for debugging. This patch
adds support for these two items in debugfs.

Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Reviewed-by: Peng Li <lipeng321@huawei.com>
Reviewed-by: Zhong Zhaohui <zhongzhaohui@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>