iio: light: as73211: New driver

Support for AMS AS73211 JENCOLOR(R) Digital XYZ Sensor.

This driver has no built-in trigger. In order for making triggered
measurements, an external (software) trigger driver like
iio-trig-hrtimer or iio-trig-sysfs is required.

The sensor supports single and continuous measurement modes. The latter
is not used by design as this would require tight timing synchronization
between hardware and driver without much benefit.

Datasheet: https://ams.com/documents/20143/36005/AS73211_DS000556_3-01.pdf


Signed-off-by: Christian Eggers <ceggers@arri.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>