net: dsa: realtek: use the same mii bus driver for both interfaces

The realtek-mdio will now use this driver instead of the generic DSA
driver ("dsa user smi"), which should not be used with OF[1].

With a single ds_ops for both interfaces, the ds_ops in realtek_priv is
no longer necessary. Now, the realtek_variant.ds_ops can be used
directly.

The realtek_priv.setup_interface() has been removed as we can directly
call the new common function.

[1] https://lkml.kernel.org/netdev/20220630200423.tieprdu5fpabflj7@bang-olufsen.dk/T/



Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>