sfc: support ndo_get_phys_port_id even when !CONFIG_SFC_SRIOV

There's no good reason why this should be an SRIOV-only thing.
Thus, also move it out of SRIOV-specific files.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>