dt-bindings: arm: at91: add Kontron's new KSwitches

The Kontron KSwitch D10 MMT series ethernet switches features a LAN9668
SoC with either 8 copper ports or 6 copper port and two SFP cages.

Signed-off-by: Michael Walle <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Nicolas Ferre <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/arm/atmel-at91.yaml

···
           - const: microchip,lan9668
           - const: microchip,lan966
 
+      - description: Kontron KSwitch D10 MMT series
+        items:
+          - enum:
+              - kontron,kswitch-d10-mmt-8g
+              - kontron,kswitch-d10-mmt-6g-2gs
+          - const: kontron,s1921
+          - const: microchip,lan9668
+          - const: microchip,lan966
+
       - items:
           - enum:
               - atmel,sams70j19