dt-bindings: i2c: Add hpe,gxp-i2c

Document compatibility string to support I2C controller
in GXP.
Signed-off-by: Nick Hawkins <nick.hawkins@hpe.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Documentation/devicetree/bindings/i2c/hpe,gxp-i2c.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/i2c/hpe,gxp-i2c.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: HPE GXP SoC I2C Controller
+
+maintainers:
+  - Nick Hawkins <nick.hawkins@hpe.com>
+
+allOf:
+  - $ref: /schemas/i2c/i2c-controller.yaml#
+
+properties:
+  compatible:
+    const: hpe,gxp-i2c
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clock-frequency:
+    default: 100000
+
+  hpe,sysreg:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description:
+      Phandle to the global status and enable interrupt registers shared
+      between each I2C engine controller instance. It enables the I2C
+      engine controller to act as both a master or slave by being able to
+      arm and respond to interrupts from its engine. Each bit in the
+      registers represent the respective bit position.
+
+required:
+  - compatible
+  - reg
+  - interrupts
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    i2c@2600 {
+        compatible = "hpe,gxp-i2c";
+        reg = <0x2500 0x70>;
+        interrupts = <9>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+        hpe,sysreg = <&sysreg_system_controller>;
+        clock-frequency = <10000>;
+
+        eeprom@50 {
+            compatible = "atmel,24c128";
+            reg = <0x50>;
+        };
+    };