net: hns3: add support for dumping MAC umv counter in debugfs

This patch adds support of dumping MAC umv counter in debugfs,
which will be helpful for debugging.

The display style is below:
$ cat umv_info
num_alloc_vport  : 2
max_umv_size     : 256
wanted_umv_size  : 256
priv_umv_size    : 85
share_umv_size   : 86
vport(0) used_umv_num : 1
vport(1) used_umv_num : 1

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>