msm-vidc: return unknown ctrl for internal cvp client

CVP clients does not set any v4l2 controls on video node.
- Remove the present controls for CVP and keep the
  unknown control alone.
- In get_ctrl calls, directly pass the base control
  inst->ctrls[0] for internal CVP session.

Change-Id: I9a1c9f4638039cd93368b6a1e8335d64985e0e3b