iio: adc: max77541: Add ADI MAX77541 ADC Support

The MAX77541 has an 8-bit Successive Approximation Register (SAR) ADC
with four multiplexers for supporting the telemetry feature.

Signed-off-by: Okan Sahin <okan.sahin@analog.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230412111256.40013-4-okan.sahin@analog.com
Signed-off-by: Lee Jones <lee@kernel.org>