net: hns3: Add support for PFC setting in TM module

This patch add a pfc_pause_en cmd, and use it to configure
PFC option according to fc_mode in hdev->tm_info.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>