realtek: rtl930x: move SerDes mapping from MDIO to PCS

realtek: rtl930x: move SerDes mapping from MDIO to PCS

For RTL930x, the SerDes MDIO driver performed a slight SerDes ID mapping
on certain conditions. Instead of keeping this mapping in the MDIO and
try to extend it for further quirks, lets just be a plain MDIO here and
let the user (PCS) deal with these complex quirks.

Drop the mapping from the SerDes MDIO driver and move it to the PCS
driver by leveraging the previously introduced SerDes operations
structure. Define separate ops which incorporate this mapping and use
those instead of the generic implementations.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21592
Signed-off-by: Robert Marko <robimarko@gmail.com>