net: sparx5: add function for RGMII port check

The lan969x device contains two RGMII port interfaces, sitting at port
28 and 29. Add function: is_port_rgmii() to the match data ops, that
checks if a given port is an RGMII port or not. For Sparx5, this
function always returns false.

Reviewed-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Tested-by: Robert Marko <robert.marko@sartura.hr>
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Link: https://patch.msgid.link/20241220-sparx5-lan969x-switch-driver-4-v5-2-fa8ba5dff732@microchip.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>