ARM: dts: am437x: replace linux,wakeup with wakeup-source property

Most of the legacy "linux,wakeup" boolean property is already replaced
with "wakeup-source". However few occurrences of old property has popped
up again, probably from the remnants in downstream trees.

Replace the legacy properties with the unified "wakeup-source" property
introduced in the commit aeda5003d0b9 ("Input: matrix_keypad - change
name of wakeup property to "wakeup-source"")

Cc: "Benoît Cousson" <[e-mail]>
Cc: Tony Lindgren <[e-mail]>
Cc: [e-mail]
Signed-off-by: Sudeep Holla <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/boot/dts/am437x-gp-evm.dts

···
 		pinctrl-0 = <&matrix_keypad_default>;
 		pinctrl-1 = <&matrix_keypad_sleep>;
 
-		linux,wakeup;
+		wakeup-source;
 
 		row-gpios = <&gpio0 3 GPIO_ACTIVE_HIGH /* Bank0, pin3 */
 				&gpio4 3 GPIO_ACTIVE_HIGH /* Bank4, pin3 */