dt-bindings: leds: mt6370: Add MediaTek MT6370 current sink type LED indicator

Add MediaTek MT6370 current sink type LED indicator binding documentation.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Link: https://lore.kernel.org/r/27df85c30277a171ae85ff6d5b7d867625765d0a.1663926551.git.chiaen_wu@richtek.com


Signed-off-by: Rob Herring <robh@kernel.org>