realtek: make use of serdes helper for Netgear GS310TP v1

realtek: make use of serdes helper for Netgear GS310TP v1

Use the new INTERNAL_PHY_SDS() helper to describe the SFP ports. With
this change the driver now knows that ports 24/26 are driven by serdes
4/5.

For the RTL838x devices this is currently only an additional information
for the mdio bus. It is not evaluated further because everything is
hardcoded.

REMARK! The original commit c829bc1f2c3c47e2 ("realtek: Add support for
Netgear S350 series switches GS308T and GS310TP") says that the SFP
ports are untested. Looking at device internal pictures from
https://techinfodepot.shoutwiki.com/wiki/Netgear_GS310TP there are no
external phys for the SFP ports. So fix port description.

Signed-off-by: Markus Stockhausen <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/18851
Signed-off-by: Robert Marko <[email protected]>