dt-bindings: arm: realtek: Document RTD1293 and Synology DS418j

Define compatible strings for Realtek RTD1293 SoC and Synology
DiskStation DS418j NAS.

Cc: info@synology.com
Acked-by: Rob Herring <robh@kernel.org>
[AF: Converted to json-schema]
Signed-off-by: Andreas Färber <afaerber@suse.de>

Documentation/devicetree/bindings/arm/realtek.yaml

@@ -14,6 +14,12 @@ properties:
     const: '/'
   compatible:
     oneOf:
+      # RTD1293 SoC based boards
+      - items:
+          - enum:
+              - synology,ds418j # Synology DiskStation DS418j
+          - const: realtek,rtd1293
+
       # RTD1295 SoC based boards
       - items:
           - enum: