realtek: decouple MDIO and ethernet devices

realtek: decouple MDIO and ethernet devices

We are lucky to have a working realtek environment. But some things where mixed
heavily. To say it clear a bus is a bus and an ethernet is an ethernet. With
the new naming conventions and defines this becomes even more obvious.

Decouple it by moving the bus specific parts out of the ethernet device. To
make the code more readable rename bus_priv variables to priv and sort variable
definitions in inverse tree order (length descending) where it makes sense.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/18402
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>