dt-bindings: arm: hpe: add GXP Support

Add support for HPE GXP. The GXP is based on the cortex a9 processor and
supports arm7.
Signed-off-by: Nick Hawkins <nick.hawkins@hpe.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Documentation/devicetree/bindings/arm/hpe,gxp.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/hpe,gxp.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: HPE BMC GXP platforms
+
+maintainers:
+  - Nick Hawkins <nick.hawkins@hpe.com>
+  - Jean-Marie Verdun <verdun@hpe.com>
+
+properties:
+  compatible:
+    oneOf:
+      - description: GXP Based Boards
+        items:
+          - enum:
+              - hpe,gxp-dl360gen10
+          - const: hpe,gxp
+
+required:
+  - compatible
+
+additionalProperties: true
+
+...