ASoC: tas2770: expose die temp to hwmon

ASoC: tas2770: expose die temp to hwmon

TAS2770 includes an ADC which reports the chip's die temperature.
As per the datasheet, the temperature in degrees Celsius is derived
by taking the raw value stored in the ADC's registers, dividing by 16,
then subtracting 93.

Create and register a hwmon device to expose the chip's die temperature
to the hwmon interface.

The ADC is shut down during software shutdown mode, and its registers
are initialised to 0 on reset. This means that the die temperature will
read -93 *C until the chip has been fully powered up at least once (e.g.
the PCM its attached to is opened). Once the chip is put into software
shutdown again, the ADC will also shut down. The last value sampled
before this happens will persist in the ADC's registers.

Co-developed-by: Martin Povišer <povik+lin@cutebit.org>
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
Link: https://patch.msgid.link/20250406-apple-codec-changes-v5-7-50a00ec850a3@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>