dt-bindings: arm: Add missing AMD Seattle SoC platforms

AMD Seattle SoC has been in use for some time, but the root compatibles
have not been documented. Add them.

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rob Herring (Arm) <[e-mail]>

Documentation/devicetree/bindings/arm/amd,seattle.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/amd,seattle.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: AMD Seattle SoC Platforms
+
+maintainers:
+  - Suravee Suthikulpanit <[e-mail]>
+  - Tom Lendacky <[e-mail]>
+
+properties:
+  $nodename:
+    const: "/"
+  compatible:
+    oneOf:
+      - description: Boards with AMD Seattle SoC
+        items:
+          - const: amd,seattle-overdrive
+          - const: amd,seattle
+
+additionalProperties: true
+...