iio: adc: ad7173: Add support for AD411x devices

Add support for AD4111/AD4112/AD4114/AD4115/AD4116.

The AD411X family encompasses a series of low power, low noise, 24-bit,
sigma-delta analog-to-digital converters that offer a versatile range of
specifications.

This family of ADCs integrates an analog front end suitable for processing
both fully differential and single-ended, bipolar voltage inputs
addressing a wide array of industrial and instrumentation requirements.

- All ADCs have inputs with a precision voltage divider with a division
  ratio of 10.
- AD4116 has 5 low level inputs without a voltage divider.
- AD4111 and AD4112 support current inputs (0 mA to 20 mA) using a 50ohm
  shunt resistor.

Signed-off-by: Dumitru Ceclan <[email protected]>
Reviewed-by: Nuno Sa <[email protected]>
Reviewed-by: David Lechner <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jonathan Cameron <[email protected]>

Author: dumitruceclan