net: dsa: microchip: clean up ksz8_reg definition macros

Remove macros that are already defined at more appropriate places.

Signed-off-by: Pieter Van Trappen <pieter.van.trappen@cern.ch>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>