dt-bindings: arm: bcm: add bindings for ASUS RT-AC3200

Add ASUS RT-AC3200 under BCM4709 based boards.
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240423-for-soc-asus-rt-ac3200-ac5300-v3-1-23d33cfafe7a@arinc9.comSigned-off-by: Florian Fainelli <florian.fainelli@broadcom.com>

Documentation/devicetree/bindings/arm/bcm/brcm,bcm4708.yaml

@@ -53,6 +53,7 @@ properties:
       - description: BCM4709 based boards
         items:
           - enum:
+              - asus,rt-ac3200
               - asus,rt-ac87u
               - buffalo,wxr-1900dhp
               - linksys,ea9200