net: hns3: Add mailbox support to VF driver

This patch adds the support of the mailbox to the VF driver. The
mailbox shall be used as an interface to communicate with the
PF driver for various purposes like {set|get} MAC related
operations, reset, link status etc. The mailbox supports both
synchronous and asynchronous command send to PF driver.

Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: lipeng <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>