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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

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

···
 		interrupts = <2 IRQ_TYPE_LEVEL_LOW>;
 		pinctrl-names = "default";
 		pinctrl-0 = <&s2mps11_irq>;
+		wakeup-source;
 
 		s2mps11_osc: clocks {
 			compatible = "samsung,s2mps11-clk";