net: hns3: refactor dump fd tcam of debugfs

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

The display style is below:
$ cat fd_tcam
read result tcam key x(31):
00000000
00000000
00000000
08000000
00000600
00000000
00000000
00000000
00000000
00000000
00000000
00000000
00000000
read result tcam key y(31):
00000000
00000000
00000000
f7ff0000
0000f900
00000000
00000000
00000000
00000000
00000000
00000000
00000000
0000fff8

Signed-off-by: Hao Chen <chenhao288@hisilicon.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>