dt-bindings: backlight: Add Texas Instruments LM3509

Add Device Tree bindings for Texas Instruments LM3509 - a
High Efficiency Boost for White LED's and/or OLED Displays

Signed-off-by: Patrick Gansterer <paroga@paroga.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20240526105136.721529-2-paroga@paroga.com


Signed-off-by: Lee Jones <lee@kernel.org>