[media] stk1160: Remove stk1160-mixer and setup internal AC97 codec automatically

Exposing all the channels of the device's internal AC97 codec to
userspace is unnecessary and confusing. Instead the driver should setup
the codec with proper values. This patch removes the mixer and sets up
the codec using optimal values, i.e. the same values set by the Windows
driver. This also makes the device work out-of-the-box, without the need
for the user to reconfigure the device every time it's plugged in.

Signed-off-by: Marcel Hasler <mahasler@gmail.com>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>