[media] au0828: explicitly identify boards with analog TV

Right now, the au0828 driver uses .tuner to detect if analog
tv is being used or not. By not filling .tuner fields at the
board struct, the I2C core can't do decisions based on it.

So, add a field to explicitly tell when analog TV is supported.

No functional changes.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>