V4L/DVB (3693): Fix msp3400c and bttv stereo/mono/bilingual detection/handling

V4L/DVB (3693): Fix msp3400c and bttv stereo/mono/bilingual detection/handling

- msp3400c did not detect the second carrier, thus being always mono.
- properly mute the msp3400c while detecting the carrier.
- fix checks on the presence of scart2/3 inputs and scart 2 output.
- implement proper audio mode fallbacks for msp3400c/d, identical to the
  way msp3400g works.
- MODE_STEREO no longer produces dual languages when set for a bilingual
  transmission, instead it falls back to LANG1. Use LANG1_LANG2 to hear
  both languages of a bilingual transmission. This is much more intuitive
  for the user and is in accordance with the preferred usage in the v4l2
  specification.
- bttv tried to implement v4l2 calls with v4l1 calls to the i2c devices,
  completely mangling the audmode/rxsubchans handling. v4l2 calls now do
  v4l2 calls to the i2c devices.
- fixed broken i2c_vidiocschan in bttv.
- add start/end lines to LOG_STATUS.

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