ARM: dts: at91: sama5d2_xplained: enable RTC wakeup

The sama5d2 Xplained can wake up with its RTC. Enable that feature.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

arch/arm/boot/dts/at91-sama5d2_xplained.dts

@@ -246,6 +246,7 @@ uart5: serial@200 {
 
 			shdwc@f8048010 {
 				atmel,shdwc-debouncer = <976>;
+				atmel,wakeup-rtc-timer;
 
 				input@0 {
 					reg = <0>;