Chrysler: allow for lower min steer speed on the way down

[adeebshihadeh]

https://github.com/commaai/openpilot/blob/b941b39c56db2d9d7f756cb0949ef6a7cf61774a/selfdrive/car/chrysler/interface.py#L35

controlsd should generically support asymmetric min steer speeds, one for engage and another for disengaging.