net: hns3: add support for dump firmware statistics by debugfs

This patch prints firmware statistics information.

debugfs command:
echo dump m7 info > cmd

estuary:/dbg/hns3/0000:7d:00.0$ echo dump m7 info > cmd
[  172.577240] hns3 0000:7d:00.0: 0x00000000  0x00000000  0x00000000
[  172.583471] hns3 0000:7d:00.0: 0x00000000  0x00000000  0x00000000
[  172.589552] hns3 0000:7d:00.0: 0x00000030  0x00000000  0x00000000
[  172.595632] hns3 0000:7d:00.0: 0x00000000  0x00000000  0x00000000
estuary:/dbg/hns3/0000:7d:00.0$

Signed-off-by: Zhongzhu Liu <liuzhongzhu@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>