ASoC: tlv320adcx140: add channel sum control

ASoC: tlv320adcx140: add channel sum control

Add control for channel summation.

3 modes are supported:

1. "Disabled": Normal operation

2. "2 Channel": Every two channels are summed and divided by 2

  Out 1 <- (CH1 + CH2) / 2
  Out 2 <- (CH1 + CH2) / 2
  Out 3 <- (CH3 + CH4) / 2
  Out 4 <- (CH3 + CH4) / 2

3. "4 Channel": Every four channels are summed and divided by 4

  Out 1 <- (CH1 + CH2 + CH3 + CH4) / 4
  Out 2 <- (CH1 + CH2 + CH3 + CH4) / 4
  Out 3 <- (CH1 + CH2 + CH3 + CH4) / 4
  Out 4 <- (CH1 + CH2 + CH3 + CH4) / 4

Signed-off-by: Emil Svendsen <emas@bang-olufsen.dk>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://patch.msgid.link/20260113-sound-soc-codecs-tvl320adcx140-v4-10-8f7ecec525c8@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>