arm64: dts: imx8mq-librem5: make the volume buttons a wakeup source

They turn on the display currently so to be consistent, let's make
them wake the system from suspend as well.
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq-librem5.dtsi

@@ -42,6 +42,7 @@ vol-down {
 			gpios = <&gpio1 17 GPIO_ACTIVE_LOW>;
 			linux,code = <KEY_VOLUMEDOWN>;
 			debounce-interval = <50>;
+			wakeup-source;
 		};
 
 		vol-up {
@@ -49,6 +50,7 @@ vol-up {
 			gpios = <&gpio1 16 GPIO_ACTIVE_LOW>;
 			linux,code = <KEY_VOLUMEUP>;
 			debounce-interval = <50>;
+			wakeup-source;
 		};
 	};