devlink: Return physical port fields only for applicable port flavours

Physical port number and split group fields are applicable only to
physical port flavours such as PHYSICAL, CPU and DSA.
Hence limit returning those values in netlink response to such port
flavours.

Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>