iio: adc: add max11205 adc driver

Adding support for max11205 16-bit single-channel ultra-low power
delta-sigma adc.
The MAX11205 is compatible with the 2-wire interface and uses
SCLK and RDY/DOUT for serial communications. In this mode, all
controls are implemented by timing the high or low phase of the SCLK.
The 2-wire serial interface only allows for data to be read out through
the RDY/DOUT output.

Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX11205.pdf
Signed-off-by: Ramona Bolboaca <ramona.bolboaca@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220831133021.215625-2-ramona.bolboaca@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>