net: dsa: microchip: add multi queue support for KSZ88X3 variants

KSZ88X3 switches support up to 4 queues. Rework ksz8795_set_prio_queue()
to support KSZ8795 and KSZ88X3 families of switches.

Per default, configure KSZ88X3 to use one queue, since it need special
handling due to priority related errata. Errata handling is implemented
in a separate patch.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>