net: dsa: microchip: Add Microchip KSZ8863 SMI based driver support

Add KSZ88X3 driver support. We add support for the KXZ88X3 three port
switches using the Microchip SMI Interface. They are supported using the
MDIO-Bitbang Interface.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>