net: dsa: microchip: ksz8: move all DSA configurations to one location

To make the code more comparable to KSZ9477 code, move DSA
configurations to the same location.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>