iio: temperature: Add MAX31865 RTD Support

This patch adds support for Maxim MAX31865 RTD temperature
sensor support.

More information can be found in:
https://datasheets.maximintegrated.com/en/ds/MAX31865.pdf



Signed-off-by: Navin Sankar Velliangiri <navin@linumiz.com>
Link: https://lore.kernel.org/r/20210824050123.71289-1-navin@linumiz.com


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