dt-bindings: display: bridge: ldb: Add an i.MX6SX entry

i.MX6SX has a single LVDS port and share a similar LDB_CTRL register
layout with i.MX8MP and i.MX93.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230404020129.509356-1-festevam@gmail.com

Documentation/devicetree/bindings/display/bridge/fsl,ldb.yaml

@@ -17,6 +17,7 @@ description: |
 properties:
   compatible:
     enum:
+      - fsl,imx6sx-ldb
       - fsl,imx8mp-ldb
       - fsl,imx93-ldb
 
@@ -64,7 +65,9 @@ allOf:
       properties:
         compatible:
           contains:
-            const: fsl,imx93-ldb
+            enum:
+              - fsl,imx6sx-ldb
+              - fsl,imx93-ldb
     then:
       properties:
         ports: