dt-bindings: fsi: Document the FSI Hub Controller

Document the FSI Hub Controller CFAM engine.
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240522192524.3286237-11-eajames@linux.ibm.comSigned-off-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/fsi/ibm,p9-fsi-controller.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/fsi/ibm,p9-fsi-controller.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: IBM FSI-attached FSI Hub Controller
+
+maintainers:
+  - Eddie James <eajames@linux.ibm.com>
+
+description:
+  The FSI Hub Controller is an FSI controller, providing a number of FSI links,
+  located on a CFAM. Therefore this node will always be a child of an FSI CFAM
+  node.
+
+properties:
+  compatible:
+    enum:
+      - ibm,p9-fsi-controller
+
+  reg:
+    items:
+      - description: FSI slave address
+
+allOf:
+  - $ref: fsi-controller.yaml#
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    fsi@3400 {
+        compatible = "ibm,p9-fsi-controller";
+        reg = <0x3400 0x400>;
+        #address-cells = <2>;
+        #size-cells = <0>;
+
+        cfam@0,0 {
+            reg = <0 0>;
+            #address-cells = <1>;
+            #size-cells = <1>;
+            chip-id = <0>;
+        };
+    };