iio: light: Added AMS tsl2591 driver implementation

iio: light: Added AMS tsl2591 driver implementation

Driver implementation for AMS/TAOS tsl2591 ambient light sensor.

This driver supports configuration via device tree and sysfs.
Supported channels for raw infrared light intensity,
raw combined light intensity and illuminance in lux.
The driver additionally supports iio events on lower and
upper thresholds.

This is a very-high sensitivity light-to-digital converter that
transforms light intensity into a digital signal.

Datasheet: https://ams.com/tsl25911#tab/documents
Signed-off-by: Joe Sandom <joe.g.sandom@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210421221330.17007-1-joe.g.sandom@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>