i40e: Add initial devlink support

Add an initial support for devlink interface to i40e driver.

Similarly to ice driver the implementation doe not enable devlink
to manage device-wide configuration and devlink instance is created
for each physical function of PCIe device.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>