dt-bindings: iio: ROHM BU27010 RGBC + flickering sensor

The ROHM BU27010 is a sensor with 6 photodiodes (red, green, blue, clear,
IR and flickering detection) with five configurable channels. Red, green
and flickering detection being always available and two out of the rest
three (blue, clear, IR) can be selected to be simultaneously measured.
Typical application is adjusting LCD/OLED backlight of TVs, mobile phones
and tablet PCs.

Add binding document for ROHM BU27010.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/717d30694ba6864b8c28772d7478bed93ea10138.1690958450.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>