ARM: dts: colibri-imx6: improve wake-up with gpio key

The pin GPIO2_IO22 externally pulls down, it is required to sequentially
connect this pin (signal WAKE_MICO#) to +3v3 and then disconnect it to
trigger a wakeup interrupt.
Adding the flag GPIO_PULL_DOWN allows the system to be woken up just
connecting the pin GPIO2_IO22 to +3v3.
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl-colibri.dtsi

@@ -38,7 +38,7 @@ gpio-keys {
 
 		wakeup {
 			debounce-interval = <10>;
-			gpios = <&gpio2 22 GPIO_ACTIVE_HIGH>; /* SODIMM 45 */
+			gpios = <&gpio2 22 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>; /* SODIMM 45 */
 			label = "Wake-Up";
 			linux,code = <KEY_WAKEUP>;
 			wakeup-source;