ASoC: tlv320aic3x: headset/button press support

- Add aic3x_set_headset_detection() function to define the headset
  detection mode for tlv32aic3x chips
- added aic3x_button_pressed()
- Read from the real-time registers in aic3x_headset_detected() to query
  headset presence without an occured interrupt

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>