ARM: dts: omap5: replace gpio-key,wakeup with wakeup-source property

Though the keyboard driver for GPIO buttons(gpio-keys) will continue to
check for/support the legacy "gpio-key,wakeup" boolean property to
enable gpio buttons as wakeup source, "wakeup-source" is the new
standard binding.

This patch replaces the legacy "gpio-key,wakeup" with the unified
"wakeup-source" property in order to avoid any further copy-paste
duplication.

Cc: "Benoît Cousson" <bcousson@baylibre.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/omap5-uevm.dts

@@ -41,7 +41,7 @@ btn1 {
 			label = "BTN1";
 			linux,code = <169>;
 			gpios = <&gpio3 19 GPIO_ACTIVE_LOW>;	/* gpio3_83 */
-			gpio-key,wakeup;
+			wakeup-source;
 			autorepeat;
 			debounce_interval = <50>;
 		};