dt-bindings: net: dsa: sf2: add BCM4908 switch binding

BCM4908 family SoCs have integrated Starfighter 2 switch.
Signed-off-by: NRafał Miłecki <rafal@milecki.pl>
Acked-by: NFlorian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20210106213202.17459-2-zajec5@gmail.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/dsa/brcm,sf2.yaml

@@ -13,6 +13,7 @@ properties:
   compatible:
     items:
       - enum:
+          - brcm,bcm4908-switch
           - brcm,bcm7278-switch-v4.0
           - brcm,bcm7278-switch-v4.8
           - brcm,bcm7445-switch-v4.0