refactor: Align drivers with Zephyr file system conventions

PR: #400

app/drivers/zephyr/dts/bindings/kscan/zmk,kscan-gpio-demux.yaml

@@ -0,0 +1,22 @@
+# Copyright (c) 2020, The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: GPIO keyboard demux controller
+
+compatible: "zmk,kscan-gpio-demux"
+
+include: kscan.yaml
+
+properties:
+  input-gpios:
+    type: phandle-array
+    required: true
+  output-gpios:
+    type: phandle-array
+    required: true
+  debounce-period:
+    type: int
+    default: 5
+  polling-interval-msec:
+    type: int
+    default: 25

app/drivers/zephyr/dts/bindings/kscan/zmk,kscan-gpio-direct.yaml

@@ -0,0 +1,16 @@
+# Copyright (c) 2020, Pete Johanson
+# SPDX-License-Identifier: MIT
+
+description: Direct GPIO keyboard KSCAN controller
+
+compatible: "zmk,kscan-gpio-direct"
+
+include: kscan.yaml
+
+properties:
+  input-gpios:
+    type: phandle-array
+    required: true
+  debounce-period:
+    type: int
+    default: 5

app/drivers/zephyr/dts/bindings/kscan/zmk,kscan-gpio-matrix.yaml

@@ -0,0 +1,25 @@
+# Copyright (c) 2020, Pete Johanson
+# SPDX-License-Identifier: MIT
+
+description: GPIO keyboard matrix controller
+
+compatible: "zmk,kscan-gpio-matrix"
+
+include: kscan.yaml
+
+properties:
+  row-gpios:
+    type: phandle-array
+    required: true
+  col-gpios:
+    type: phandle-array
+    required: true
+  debounce-period:
+    type: int
+    default: 5
+  diode-direction:
+    type: string
+    default: row2col
+    enum:
+      - row2col
+      - col2row