refactor: Add kscan sideband behavior driver

* Instead of gpio key behavior trigger, add new kscan driver that
  decorates/wraps a given kscan driver and will invoke basic system
  behavior assigned to a given row + column, without the need for keymap
  mapping in the matrix transform, bypassing keymaps entirely.

app/dts/bindings/kscan/zmk,kscan-sideband-behaviors.yaml

@@ -0,0 +1,29 @@
+# Copyright (c) 2023, The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: |
+  kscan sideband behavior runner. Only basic system behavior should be used,
+  since no keymap processing occurs when using them.
+
+compatible: "zmk,kscan-sideband-behaviors"
+
+include: [kscan.yaml]
+
+properties:
+  kscan:
+    type: phandle
+    required: true
+
+child-binding:
+  description: "A sideband behavior tied to a row/column pair"
+
+  properties:
+    row:
+      type: int
+      required: true
+    column:
+      type: int
+      required: true
+    bindings:
+      type: phandle-array
+      required: true

app/dts/bindings/zmk,gpio-key-behavior-trigger.yaml

@@ -1,31 +0,0 @@
-# Copyright (c) 2023 The ZMK Contributors
-# SPDX-License-Identifier: MIT
-
-description: |
-  Driver for a dedicated key for invoking a connected behavior.
-
-compatible: "zmk,gpio-key-behavior-trigger"
-
-include: base.yaml
-
-properties:
-  key:
-    type: phandle
-    required: true
-    description: The GPIO key that triggers wake via interrupt
-  bindings:
-    type: phandle
-    required: true
-    description: The behavior to invoke when the GPIO key is pressed
-  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.