dt-bindings: pwm: Add compatible for Mediatek MT8188

Add dt-binding documentation of pwm for MediaTek MT8188 SoC.
Signed-off-by: xinlei lee <xinlei.lee@mediatek.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/mediatek,pwm-disp.yaml

@@ -27,6 +27,7 @@ properties:
       - items:
           - enum:
               - mediatek,mt8186-disp-pwm
+              - mediatek,mt8188-disp-pwm
               - mediatek,mt8192-disp-pwm
               - mediatek,mt8195-disp-pwm
           - const: mediatek,mt8183-disp-pwm