dt-bindings: iio: temperature: add MAXIM max31865 support

Add DT bindings for MAXIM max31865 RTD sensor.

Signed-off-by: Navin Sankar Velliangiri <navin@linumiz.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210824050650.72619-1-navin@linumiz.com


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