dt-bindings: mediatek: add dither description for mt8183 display

Update device tree binding documention for the display subsystem for
Mediatek MT8183 SOCs
Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.com>
Reviewed-by: Rob Herring <robh at kernel.org>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

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

@@ -33,6 +33,7 @@ Required properties (all function blocks):
 	"mediatek,<chip>-disp-wdma"  		- write DMA
 	"mediatek,<chip>-disp-ccorr"            - color correction
 	"mediatek,<chip>-disp-color" 		- color processor
+	"mediatek,<chip>-disp-dither"           - dither
 	"mediatek,<chip>-disp-aal"   		- adaptive ambient light controller
 	"mediatek,<chip>-disp-gamma" 		- gamma correction
 	"mediatek,<chip>-disp-merge" 		- merge streams from two RDMA sources