feat(drivers): Driver for MAX7318 GPIO expander (#1295)

Add driver for max7318 i2c gpio expander

Co-authored-by: Pete Johanson <peter@peterjohanson.com>

app/drivers/zephyr/dts/bindings/gpio/maxim,max7318.yaml

@@ -0,0 +1,29 @@
+#
+# Copyright (c) 2022 The ZMK Contributors
+#
+# SPDX-License-Identifier: MIT
+#
+
+description: >
+    This is a representation of the Maxim MAX7318 I2C Gpio Expander.
+
+compatible: "maxim,max7318"
+
+include: [gpio-controller.yaml, i2c-device.yaml]
+
+properties:
+    label:
+      required: true
+
+    "#gpio-cells":
+      const: 2
+
+    ngpios:
+      type: int
+      required: true
+      const: 16
+      description: Number of gpios supported
+
+gpio-cells:
+  - pin
+  - flags