dt-bindings: iio: light: add Broadcom APDS9999

dt-bindings: iio: light: add Broadcom APDS9999

Add Device Tree binding for the Broadcom APDS9999 ambient light
and proximity sensor. A separate binding file is used rather
than merging with avago,apds9300.yaml because the APDS9999
has an additional vcsel-supply for the VCSEL.

The APDS9999 features individual R, G, B, and IR channels with
a green channel that uses optical coating to approximate the
human eye spectral response for ALS/lux measurements. Calibrated
RGB color sensing is not yet implemented in the driver.

Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>