[media] mxb: fix audio handling

Instead of using custom ioctls use the VIDIOC_ENUM/G/S/_AUDIO ioctls.
Also send the same audio to both CDROM-out and line-out.

This is what you would expect and anyway, the CDROM-out connector is unlikely
to be used these days as it is obsolete.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>