dt-bindings: iommu: apple,sart: Add apple,t6020-sart compatible

"apple,t6020-sart" as found in Apple's M2 Pro/Max/Ultra SoCs is
compatible with SART3 used in t6000. Add its per-SoC compatible to allow
a distinction should it become necessary.

Reviewed-by: Neal Gompa <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Janne Grunau <[e-mail]>

Documentation/devicetree/bindings/iommu/apple,sart.yaml

···
   compatible:
     oneOf:
       - items:
-          - const: apple,t8112-sart
+          - enum:
+              - apple,t6020-sart
+              - apple,t8112-sart
           - const: apple,t6000-sart
       - enum:
           - apple,t6000-sart