drivers: iio: chemical: Add support for Sensirion SCD4x CO2 sensor

drivers: iio: chemical: Add support for Sensirion SCD4x CO2 sensor

This is a driver for the SCD4x CO2 sensor from Sensirion. The sensor is
able to measure CO2 concentration, temperature and relative humdity.
The sensor uses a photoacoustic principle for measuring CO2 concentration.
An I2C interface is supported by this driver in order to communicate with
the sensor.

Signed-off-by: Roan van Dijk <roan@protonic.nl>
Link: https://lore.kernel.org/r/20211008101706.755942-4-roan@protonic.nl
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>