nfp: wire get_phys_port_name on representors

Make nfp_port_get_phys_port_name() support new port types and
wire it up to representors' struct net_device_ops.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>