[media] dsbr100: clean up and update to the latest v4l2 framework

This driver now complies with the v4l2-compliance tests and uses the v4l2
frameworks correctly.

It has been tested with the radio-keene FM transmitter as well.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>