dt-bindings: iio: afe: add bindings for temperature-sense-rtd

dt-bindings: iio: afe: add bindings for temperature-sense-rtd

An ADC is often used to measure other quantities indirectly. This
binding describe one case, the measurement of a temperature through the
voltage across an RTD resistor such as a PT1000.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220213025739.2561834-10-liambeguin@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>