iio: potentiometer: Add driver support for AD5110

iio: potentiometer: Add driver support for AD5110

The AD5110/AD5112/AD5114 provide a nonvolatile solution
for 128-/64-/32-position adjustment applications, offering
guaranteed low resistor tolerance errors of ±8% and up to
±6 mA current density.

Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/AD5110_5112_5114.pdf
Signed-off-by: Mugilraj Dhavachelvan <dmugil2000@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210814175607.48399-3-dmugil2000@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>