net: dsa: microchip: remove the struct ksz8

This patch removes the struct ksz8 from ksz8.h which is no longer
needed. The platform bus specific details are now deferenced through
dev->priv.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>