dt-bindings: display: mediatek: update dpi supported chips

Add descriptions about supported chips, including MT2701 & MT8173 &
mt8183

Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

Documentation/devicetree/bindings/display/mediatek/mediatek,dpi.txt

@@ -7,6 +7,7 @@ output bus.
 
 Required properties:
 - compatible: "mediatek,<chip>-dpi"
+  the supported chips are mt2701 , mt8173 and mt8183.
 - reg: Physical base address and length of the controller's registers
 - interrupts: The interrupt signal from the function block.
 - clocks: device clocks