dt-bindings: iio: light: Support ROHM BU27034

ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes
capable of detecting a very wide range of illuminance. Typical application
is adjusting LCD and backlight power of TVs and mobile phones.

Add dt-bindings.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/66a222574176ee2adbfccf6d9a591c04571a18d9.1680263956.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>