dt-bindings: mediatek: add ovl_2l 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@kernel.org>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

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

@@ -27,19 +27,20 @@ Documentation/devicetree/bindings/display/mediatek/mediatek,dpi.txt.
 
 Required properties (all function blocks):
 - compatible: "mediatek,<chip>-disp-<function>", one of
-	"mediatek,<chip>-disp-ovl"   - overlay (4 layers, blending, csc)
-	"mediatek,<chip>-disp-rdma"  - read DMA / line buffer
-	"mediatek,<chip>-disp-wdma"  - write DMA
-	"mediatek,<chip>-disp-color" - color processor
-	"mediatek,<chip>-disp-aal"   - adaptive ambient light controller
-	"mediatek,<chip>-disp-gamma" - gamma correction
-	"mediatek,<chip>-disp-merge" - merge streams from two RDMA sources
-	"mediatek,<chip>-disp-split" - split stream to two encoders
-	"mediatek,<chip>-disp-ufoe"  - data compression engine
-	"mediatek,<chip>-dsi"        - DSI controller, see mediatek,dsi.txt
-	"mediatek,<chip>-dpi"        - DPI controller, see mediatek,dpi.txt
-	"mediatek,<chip>-disp-mutex" - display mutex
-	"mediatek,<chip>-disp-od"    - overdrive
+	"mediatek,<chip>-disp-ovl"   		- overlay (4 layers, blending, csc)
+	"mediatek,<chip>-disp-ovl-2l"           - overlay (2 layers, blending, csc)
+	"mediatek,<chip>-disp-rdma"  		- read DMA / line buffer
+	"mediatek,<chip>-disp-wdma"  		- write DMA
+	"mediatek,<chip>-disp-color" 		- color processor
+	"mediatek,<chip>-disp-aal"   		- adaptive ambient light controller
+	"mediatek,<chip>-disp-gamma" 		- gamma correction
+	"mediatek,<chip>-disp-merge" 		- merge streams from two RDMA sources
+	"mediatek,<chip>-disp-split" 		- split stream to two encoders
+	"mediatek,<chip>-disp-ufoe"  		- data compression engine
+	"mediatek,<chip>-dsi"        		- DSI controller, see mediatek,dsi.txt
+	"mediatek,<chip>-dpi"        		- DPI controller, see mediatek,dpi.txt
+	"mediatek,<chip>-disp-mutex" 		- display mutex
+	"mediatek,<chip>-disp-od"    		- overdrive
   the supported chips are mt2701, mt2712 and mt8173.
 - reg: Physical base address and length of the function block register space
 - interrupts: The interrupt signal from the function block (required, except for