feat: Add soft on/off support.

Initial work on a soft on/off support for ZMK. Triggering soft off
puts the device into deep sleep with only a specific GPIO pin
configured to wake the device, avoiding waking from other key
presses in the matrix like the normal deep sleep.

Co-authored-by: Cem Aksoylar <caksoylar@users.noreply.github.com>

app/dts/behaviors.dtsi

@@ -20,3 +20,4 @@
 #include <behaviors/backlight.dtsi>
 #include <behaviors/macros.dtsi>
 #include <behaviors/mouse_key_press.dtsi>
+#include <behaviors/soft_off.dtsi>

app/dts/behaviors/soft_off.dtsi

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2023 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+/ {
+    behaviors {
+        /omit-if-no-ref/ soft_off: behavior_soft_off {
+            compatible = "zmk,behavior-soft-off";
+            label = "SOFTOFF";
+            #binding-cells = <0>;
+        };
+    };
+};

app/dts/bindings/zmk,behavior-key-scanned.yaml

@@ -0,0 +1,31 @@
+# Copyright (c) 2023 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: |
+  Driver for a dedicated key triggered by matrix scanning for invoking a connected behavior.
+
+compatible: "zmk,behavior-key-scanned"
+
+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 GPIO key that triggers wake via interrupt
+  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.

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

@@ -0,0 +1,31 @@
+# Copyright (c) 2023 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: |
+  Driver for a dedicated key for invoking a connected behavior.
+
+compatible: "zmk,behavior-key"
+
+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 GPIO key that triggers wake via interrupt
+  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.

app/dts/bindings/zmk,soft-off-wakeup-sources.yaml

@@ -0,0 +1,14 @@
+# Copyright (c) 2023 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: |
+  Description of all possible wakeup-sources from a forces
+  soft-off state.
+
+compatible: "zmk,soft-off-wakeup-sources"
+
+properties:
+  wakeup-sources:
+    type: phandles
+    required: true
+    description: List of wakeup-sources that should be enabled to wake the system from forces soft-off state.

app/dts/bindings/zmk,wakeup-trigger-key.yaml

@@ -0,0 +1,18 @@
+# Copyright (c) 2023 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: |
+  Driver for a dedicated key for waking the device from sleep
+
+compatible: "zmk,wakeup-trigger-key"
+
+include: base.yaml
+
+properties:
+  trigger:
+    type: phandle
+    required: true
+    description: The GPIO key that triggers wake via interrupt
+  extra-gpios:
+    type: phandle-array
+    description: Optional set of pins that should be set active before sleeping.