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

The RTC on S2MPS11 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/20210420164943.11152-8-krzysztof.kozlowski@canonical.com

arch/arm/boot/dts/exynos5420-arndale-octa.dts

@@ -352,6 +352,7 @@ pmic@66 {
 		interrupts = <2 IRQ_TYPE_LEVEL_LOW>;
 		pinctrl-names = "default";
 		pinctrl-0 = <&s2mps11_irq>;
+		wakeup-source;
 
 		s2mps11_osc: clocks {
 			compatible = "samsung,s2mps11-clk";