dt-bindings: soc: nuvoton: Add NPCM GFXI

Add dt-bindings document for Graphics Core Information (GFXI) node. It
is used by NPCM video driver to retrieve Graphics core information.
Signed-off-by: Marvin Lin <milkfafa@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Documentation/devicetree/bindings/soc/nuvoton/nuvoton,gfxi.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/soc/nuvoton/nuvoton,gfxi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Graphics Core Information block in Nuvoton SoCs
+
+maintainers:
+  - Joseph Liu <kwliu@nuvoton.com>
+  - Marvin Lin <kflin@nuvoton.com>
+
+description:
+  The Graphics Core Information (GFXI) are a block of registers in Nuvoton SoCs
+  that analyzes Graphics core behavior and provides information in registers.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - nuvoton,npcm750-gfxi
+          - nuvoton,npcm845-gfxi
+      - const: syscon
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    gfxi: gfxi@e000 {
+      compatible = "nuvoton,npcm750-gfxi", "syscon";
+      reg = <0xe000 0x100>;
+    };