net: hns3: refactor dump serv info of debugfs

mainline inclusion
from mainline-master
commit 058c3be9
category: feature
bugzilla: 173966
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=058c3be95235a12953d6533ef1486dc3d5879688



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

The display style is below:
$ cat service_task_info
local_clock: [  114.203321]
delta: 784(ms)
last_service_task_processed: 4294918512(jiffies)
last_service_task_cnt: 4

Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Yongxin Li <liyongxin1@huawei.com>
Signed-off-by: Junxin Chen <chenjunxin1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>