dt-bindings: fsi: Document the IBM SCOM engine

The SCOM engine provides an interface to the POWER processor PIB
(Pervasive Interconnect Bus).
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240522192524.3286237-4-eajames@linux.ibm.comSigned-off-by: Rob Herring (Arm) <robh@kernel.org>

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

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/fsi/ibm,p9-scom.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: IBM FSI-attached SCOM engine
+
+maintainers:
+  - Eddie James <eajames@linux.ibm.com>
+
+description:
+  The SCOM engine is an interface to the POWER processor PIB (Pervasive
+  Interconnect Bus). This node will always be a child of an FSI CFAM node.
+
+properties:
+  compatible:
+    enum:
+      - ibm,p9-scom
+      - ibm,i2cr-scom
+
+  reg:
+    items:
+      - description: FSI slave address
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    scom@1000 {
+        compatible = "ibm,p9-scom";
+        reg = <0x1000 0x400>;
+    };