V4L/DVB (11276): tvaudio: add tda9875 support.

This change allows bttv to use tvaudio for this device. Since this device
has the same i2c address as the tda9874 we need to support both in the same
tvaudio driver. This makes it possible for tvaudio to detect which chip is
used. Originally the tda9875 was only available in the dedicated tda9875
driver, but that makes life very hard for bttv since loading tvaudio might
misdetect a tda9875 as a tda9874.

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