[media] radio-mr800: cleanup and have it comply to the V4L2 API

Implement the control framework and update to the latest V4L2 framework.
The v4l2-compliance tool now runs without errors.
Fixed bad g/s_tuner handling with respect to mono/stereo.
Support control events.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>