dt-bindings: arm: add BCM6846 SoC to device tree binding document

Add BCM6846 SoC device tree description to bcmbca binding document.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: William Zhang <william.zhang@broadcom.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/arm/bcm/brcm,bcmbca.yaml

@@ -49,6 +49,13 @@ properties:
           - const: brcm,bcm63178
           - const: brcm,bcmbca
 
+      - description: BCM6846 based boards
+        items:
+          - enum:
+              - brcm,bcm96846
+          - const: brcm,bcm6846
+          - const: brcm,bcmbca
+
       - description: BCM6858 based boards
         items:
           - enum: