iio: temperature: Add MCP9600 thermocouple EMF converter

Add support for the MCP9600 thermocouple electromotive force converter. The sensor has  integrated cold junction compensation and a typical accuracy of 0.5 degrees Celsius. The driver supports a resolution of 0.0625 degrees Celsius.

Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/MCP960X-Data-Sheet-20005426.pdf
Signed-off-by: Andrew Hepp <andrew.hepp@ahepp.dev>
Link: https://lore.kernel.org/r/20231025233153.5454-2-andrew.hepp@ahepp.dev
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>