net: hns3: add support for PTP

Adds PTP support for HNS3 ethernet driver.

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>