ARM: dts: exynos: enable PMIC wakeup from suspend on Arndale

The RTC on S5M8767 PMIC can wakeup the system from suspend to RAM.
Add a generic property for this.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210420164943.11152-3-krzysztof.kozlowski@canonical.com

arch/arm/boot/dts/exynos5250-arndale.dts

@@ -218,6 +218,7 @@ pmic@66 {
 		interrupts = <2 IRQ_TYPE_LEVEL_LOW>;
 		pinctrl-names = "default";
 		pinctrl-0 = <&s5m8767_irq>;
+		wakeup-source;
 
 		vinb1-supply = <&main_dc_reg>;
 		vinb2-supply = <&main_dc_reg>;