net: sparx5: use SPX5_CONST for constants which already have a symbol

Now that we have indentified all the chip constants, update the use of
them where a symbol is already defined for the constant.

Reviewed-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>