net: microchip: sparx5: Adding KUNIT test VCAP model

This provides a test VCAP model for use in a KUNIT test.  The model
provides 3 different VCAP types for better test coverage.

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