Radio devices have weird side-effects when used with combined TV/radio
tuners and the V4L2 spec is ambiguous on how it should work. This results
in inconsistent driver behavior which makes life hard for everyone.

Be more strict in when and how the switch between radio and tv mode
takes place and make sure all drivers behave the same.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>