net: hns3: refactor dump bd info of debugfs

Currently, the debugfs command for bd info is implemented
by "echo xxxx > cmd", and record the information in dmesg.
It's unnecessary and heavy.

To improve it, add two debugfs directories "tx_bd_info" and
"rx_bd_info", and create a file for each queue under these
two directories, and query the bd info of specific queue by
"cat tx_bd_info/tx_bd_queue*" or "cat rx_bd_info/rx_bd_queue*",
return the result to userspace, rather than record in dmesg.

The display style is below:
$ cat rx_bd_info/rx_bd_queue0
Queue 0 rx bd info:
BD_IDX   L234_INFO  PKT_LEN   SIZE...
0        0x0             60     60...
1        0x0           1512   1512...

$ cat tx_bd_info/tx_bd_queue0
Queue 0 tx bd info:
BD_IDX     ADDRESS  VLAN_TAG  SIZE...
0          0x0          0        0...
1          0x0          0        0...

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