V4L/DVB (11282): saa7134: add RDS support.

The Terratec Cinergy 600 TV MK3 supports the RDS decoder saa6588.
Add support to saa7134 for such devices.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>