dts: bindings: test: complete bindings for gpio expander

These need to be gpio controllers and have the necessary specifier
properties for use in gpio specifiers.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

dts/bindings/test/vnd,gpio-expander-common.yaml

@@ -0,0 +1,20 @@
+# Copyright (c) 2020 Nordic Semiconductor ASA
+# SPDX-License-Identifier: Apache-2.0
+
+description: Test GPIO node
+
+include: [gpio-controller.yaml, base.yaml]
+
+properties:
+    reg:
+      required: true
+
+    label:
+      required: true
+
+    "#gpio-cells":
+      const: 2
+
+gpio-cells:
+  - pin
+  - flags

dts/bindings/test/vnd,gpio-expander-i2c.yaml

@@ -5,4 +5,4 @@ description: GPIO expander via I2C
 
 compatible: "vnd,gpio-expander"
 
-include: i2c-device.yaml
+include: ["vnd,gpio-expander-common.yaml", i2c-device.yaml]

dts/bindings/test/vnd,gpio-expander-spi.yaml

@@ -5,4 +5,4 @@ description: GPIO expander via SPI
 
 compatible: "vnd,gpio-expander"
 
-include: spi-device.yaml
+include: ["vnd,gpio-expander-common.yaml", spi-device.yaml]

tests/lib/devicetree/api/app.overlay

@@ -155,6 +155,8 @@
 			};
 
 			gpio@11 {
+				gpio-controller;
+				#gpio-cells = <2>;
 				compatible = "vnd,gpio-expander";
 				reg = <0x11>;
 				label = "TEST_EXPANDER_I2C";
@@ -207,6 +209,8 @@
 			};
 
 			gpio@2 {
+				gpio-controller;
+				#gpio-cells = <2>;
 				compatible = "vnd,gpio-expander";
 				reg = <2>;
 				label = "TEST_EXPANDER_SPI";