net: hns3: Implement shutdown ops in hns3 pci driver

This patch implements shutdown ops in hns3 pci driver, which
unloads the hns3 driver and set the power state to D3hot.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>