refactor: Move drivers into properly module.

* Align our driver module layout to properly match Zephyr conventions,
  allowing proper CMake setup to amend the library for each type of driver.

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

@@ -0,0 +1,37 @@
+# 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
+    required: false
+    deprecated: true
+    description: Deprecated. Use debounce-press-ms and debounce-release-ms instead.
+  debounce-press-ms:
+    type: int
+    default: 5
+    description: Debounce time for key press in milliseconds. Use 0 for eager debouncing.
+  debounce-release-ms:
+    type: int
+    default: 5
+    description: Debounce time for key release in milliseconds.
+  debounce-scan-period-ms:
+    type: int
+    default: 1
+    description: Time between reads in milliseconds when any key is pressed.
+  poll-period-ms:
+    type: int
+    default: 10
+    description: Time between reads in milliseconds when no key is pressed and ZMK_KSCAN_DIRECT_POLLING is enabled.
+  toggle-mode:
+    type: boolean
+    description: Enable toggle-switch mode.

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

@@ -0,0 +1,43 @@
+# 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
+    required: false
+    deprecated: true
+    description: Deprecated. Use debounce-press-ms and debounce-release-ms instead.
+  debounce-press-ms:
+    type: int
+    default: 5
+    description: Debounce time for key press in milliseconds. Use 0 for eager debouncing.
+  debounce-release-ms:
+    type: int
+    default: 5
+    description: Debounce time for key release in milliseconds.
+  debounce-scan-period-ms:
+    type: int
+    default: 1
+    description: Time between reads in milliseconds when any key is pressed.
+  poll-period-ms:
+    type: int
+    default: 10
+    description: Time between reads in milliseconds when no key is pressed and ZMK_KSCAN_MATRIX_POLLING is enabled.
+  diode-direction:
+    type: string
+    default: row2col
+    enum:
+      - row2col
+      - col2row