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OPT4060 driver
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1. Overview
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This driver supports the Texas Instrument RGBW high resolution color sensor over
I2C.
https://www.ti.com/lit/gpn/opt4060

The driver supports:
- Raw values for red, green, blue and clear.
- Illuminance values.
- Scaled color values for red, green and blue.
- IIO events for thresholds.
- IIO triggered buffer using both its own data ready trigger and triggers from
other drivers.

2. Illuminance calculation
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Illuminance is calculated using the wide spectrum green channel.

lux = GREEN_RAW x 2.15e-3

The value is accessed from:
/sys/bus/iio/devices/iio:deviceX/in_illuminance_input

See section 8.4.5.2 in the data sheet for additional details.

3. Color scale values
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The sensor has different sensitivity for the different color components and
compensating factors are exposed from the driver.

The values are accessed from:
/sys/bus/iio/devices/iio:deviceX/in_intensity_red_scale
/sys/bus/iio/devices/iio:deviceX/in_intensity_green_scale
/sys/bus/iio/devices/iio:deviceX/in_intensity_blue_scale

A userspace application can multiply the raw values with the scale values so
that for a particular test light source, typically white, the measurement
intensity is the same across the different color channels. This is calculated
in the following way:

R = RED_RAW x SCALE_RED(2.4)
G = GREEN_RAW x SCALE_GREEN(1.0)
B = BLUE_RAW x SCALE_BLUE(1.3)

The data sheet suggests using the scaled values to normalize the scaled R, G
and B values. This is useful to get a value for the ratio between colors
independent of light intensity. A userspace application can do this in the
following way:

R_NORMALIZED = R / (R + G + B)
G_NORMALIZED = G / (R + G + B)
B_NORMALIZED = B / (R + G + B)

See section 8.4.5.2 in the data sheet for additional details.
