Make DUT variant configurable

[Blebowski]

At the moment, DUT version is hard-coded to CAN FD Enabled, therefore always tests for CAN FD enabled will be executed.
Extend this to cover also CAN FD Tolerant and CAN 2.0.

This setting shall be configurable from TB via VPI interface.

DUT Interface will need to have a function that will configure the DUT variant.