dt-bindings: apple,aic: Add affinity description for per-cpu pseudo-interrupts

Some of the FIQ per-cpu pseudo-interrupts are better described with
a specific affinity, the most obvious candidate being the CPU PMUs.

Augment the AIC binding to be able to specify that affinity in the
interrupt controller node.

Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

Documentation/devicetree/bindings/interrupt-controller/apple,aic.yaml

···
   power-domains:
     maxItems: 1
 
+  affinities:
+    type: object
+    additionalProperties: false
+    description:
+      FIQ affinity can be expressed as a single "affinities" node,
+      containing a set of sub-nodes, one per FIQ with a non-default
+      affinity.
+    patternProperties:
+      "^.+-affinity$":
+        type: object
+        additionalProperties: false
+        properties:
+          apple,fiq-index:
+            description:
+              The interrupt number specified as a FIQ, and for which
+              the affinity is not the default.
+            $ref: /schemas/types.yaml#/definitions/uint32
+            maximum: 5
+
+          cpus:
+            $ref: /schemas/types.yaml#/definitions/phandle-array
+            description:
+              Should be a list of phandles to CPU nodes (as described in
+              Documentation/devicetree/bindings/arm/cpus.yaml).
+
+        required:
+          - fiq-index
+          - cpus
+
 required:
   - compatible
   - '#interrupt-cells'