V4L/DVB (11394): cx88: Add support for stereo and sap detection for A2

The patch implements reliable stereo and sap detection for the A2 sound
standard.  This is achieved by processing the samples of the audio RDS fifo of
the cx2388x chip. A2M, EIAJ and BTSC stereo/sap detection is also possible with
this new approach, but it's not implemented yet. Stereo detection when alsa
handles the sound also does not work yet.

Signed-off-by: Marton Balint <cus@fazekas.hu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>