saa6588 can also be used by other drivers than just bttv. Move it to a
new RDS decoders category and add it as helper chip to bttv.
Signed-off-by: NHans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>