iio: adc: Add support for the GE HealthCare PMC ADC

The GE HealthCare PMC Analog to Digital Converter (ADC) is a 16-Channel
(voltage and current), 16-Bit ADC with an I2C Interface.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Ian Ray <ian.ray@gehealthcare.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20241003114641.672086-4-herve.codina@bootlin.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>