sensorservice: Don't replace HAL orientation sensor

* Previously HAL orientation sensor would always be replaced if the HAL
  did not provide a rotation vector sensor as well. Practically no HAL
  does, so the virtual sensor would always replace it.
* Add the virtual sensor only if the HAL does not provide it.

Change-Id: I50ad2cd6c60b53eddc4c6854997ec2e3dbff0d1a