feat(shields): Add soft-off to the nrf52840dk ZMK Uno

* Use Button 1 for soft off on the nrf52840 when using the ZMK Uno
  shield.

app/boards/shields/zmk_uno/boards/nrf52840dk_nrf52840.overlay

@@ -12,6 +12,15 @@
             bias-pull-up;
         };
     };
+
+    qdec_sleep: qdec_sleep {
+        group1 {
+            psels = <NRF_PSEL(QDEC_A, 1, 11)>,
+                    <NRF_PSEL(QDEC_B, 1, 10)>;
+            bias-pull-up;
+            low-power-enable;
+        };
+    };
 };
 
 // Set up the QDEC hardware based driver and give it the same label as the deleted node.
@@ -20,6 +29,38 @@ encoder: &qdec0 {
     led-pre = <0>;
     steps = <80>;
     pinctrl-0 = <&qdec_default>;
-    pinctrl-1 = <&qdec_default>;
+    pinctrl-1 = <&qdec_sleep>;
     pinctrl-names = "default", "sleep";
 };
+
+/ {
+    behaviors {
+        soft_off: soft_off {
+            compatible = "zmk,behavior-soft-off";
+            #binding-cells = <0>;
+            status = "okay";
+        };
+    };
+
+    wakeup_source: wakeup_source {
+        compatible = "zmk,wakeup-trigger-key";
+        status = "okay";
+
+        trigger = <&button0>;
+        wakeup-source;
+    };
+
+    soft_off_wakers {
+        compatible = "zmk,soft-off-wakeup-sources";
+        status = "okay";
+
+        wakeup-sources = <&wakeup_source>;
+    };
+
+    soft_off_behavior_key {
+        compatible = "zmk,behavior-key";
+        status = "okay";
+        bindings = <&soft_off>;
+        key = <&button0>;
+    };
+};

app/boards/shields/zmk_uno/zmk_uno.dtsi

@@ -124,6 +124,7 @@ nice_view_spi: &arduino_spi {
 
     kscan_matrix: kscan_matrix {
         compatible = "zmk,kscan-gpio-matrix";
+        wakeup-source;
 
         diode-direction = "col2row";
 
@@ -141,6 +142,7 @@ nice_view_spi: &arduino_spi {
 
     kscan_direct: kscan_direct {
         compatible = "zmk,kscan-gpio-direct";
+        wakeup-source;
         status = "disabled";
 
         input-gpios