dt-bindings: spmi: apple,spmi: Add t6020-spmi compatible

After discussion with the devicetree maintainers we agreed to not extend
lists with the generic compatible "apple,spmi" anymore [1]. Use
"apple,t8103-spmi" as base compatible as it is the SoC the driver and
bindings were written for.

The SPMI controller on Apple M2 Pro/Max/Ultra is compatible to
"apple,t8103-spmi" so add its per-SoC compatible with the former as
fallback used by the existing driver.

[1]: https://lore.kernel.org/asahi/12ab93b7-1fc2-4ce0-926e-c8141cfe81bf@kernel.org/

Reviewed-by: Neal Gompa <neal@gompa.dev>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Janne Grunau <j@jannau.net>

Documentation/devicetree/bindings/spmi/apple,spmi.yaml

@@ -16,12 +16,17 @@ allOf:
 
 properties:
   compatible:
-    items:
-      - enum:
-          - apple,t8103-spmi
-          - apple,t6000-spmi
-          - apple,t8112-spmi
-      - const: apple,spmi
+    oneOf:
+      - items:
+          - const: apple,t6020-spmi
+          - const: apple,t8103-spmi
+      - items:
+          - enum:
+              # Do not add additional SoC to this list.
+              - apple,t8103-spmi
+              - apple,t6000-spmi
+              - apple,t8112-spmi
+          - const: apple,spmi
 
   reg:
     maxItems: 1