net: hns3: refactor dump m7 info of debugfs

Currently, the debugfs command for m7 info is implemented by
"echo xxxx > cmd", and record the information in dmesg. It's
unnecessary and heavy. To improve it, create a single file
"imp_info" for it, and query it by command "cat imp_info",
return the result to userspace, rather than record in dmesg.

The display style is below:
$cat imp_info
offset | data
0x0000 | 0x00000000  0x00000000
0x0008 | 0x00000000  0x00000000
0x0010 | 0x00000000  0x00000001
0x0018 | 0x00000000  0x00000000
0x0020 | 0x00000000  0x00000000
0x0028 | 0x00000000  0x00000000
0x0030 | 0x00000000  0x00000000

Signed-off-by: Jiaran Zhang <zhangjiaran@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>