[media] saa6588: rename rds.h to saa6588.h

The naming of the media/rds.h header suggested that it was a generic
RDS header, when in fact it is just a saa6588 module API that is
internal to the kernel.

Rename the header and the struct and defines in it to make this clear.

Also removed the header include in radio-si470x.h (not used anymore)
and from ioctl-number.txt (it's internal to the kernel and never called
from userspace).

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

Documentation/ioctl/ioctl-number.txt

@@ -155,7 +155,6 @@ Code  Seq#(hex)	Include File		Comments
 'Q'	all	linux/soundcard.h
 'R'	00-1F	linux/random.h		conflict!
 'R'	01	linux/rfkill.h		conflict!
-'R'	01-0F	media/rds.h		conflict!
 'R'	C0-DF	net/bluetooth/rfcomm.h
 'S'	all	linux/cdrom.h		conflict!
 'S'	80-81	scsi/scsi_ioctl.h	conflict!