net: microchip: sparx5: Adding IS2 VCAP register interface

This adds the register interface needed to access the Sparx5 Ingress Stage
2 VCAP (IS2).

The Sparx5 Chip Register Model can be browsed at this location:
https://github.com/microchip-ung/sparx-5_reginfo

Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>