dt-bindings: leds-lp55xx: Add ti,charge-pump-mode

Add a binding to configure the internal charge pump for lp55xx.

Signed-off-by: Maarten Zanders <maarten.zanders@mind.be>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230421075305.37597-2-maarten.zanders@mind.be