V4L/DVB (5323): Updated support for tuner callbacks

V4L/DVB (5323): Updated support for tuner callbacks

This change supplies a more generic version of the tuner callback.
The tuner struct now has a function pointer
  int (*tuner_callback) (void *dev, int command, int arg)
additionally to a int config parameter.
both can be set through the TUNER_SET_TYPE_ADDR client call.
Note that the meaning of the parameters depend on the tuner type.

Signed-off-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>