dt-bindings: phy: Add compatible for Mediatek MT8188

Add dt-binding documentation of dsi-phy for MediaTek MT8188 SoC.
Signed-off-by: Shuijing Li <shuijing.li@mediatek.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230908075310.17825-1-shuijing.li@mediatek.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/phy/mediatek,dsi-phy.yaml

@@ -30,6 +30,7 @@ properties:
           - const: mediatek,mt8173-mipi-tx
       - items:
           - enum:
+              - mediatek,mt8188-mipi-tx
               - mediatek,mt8365-mipi-tx
           - const: mediatek,mt8183-mipi-tx
       - const: mediatek,mt2701-mipi-tx