ARM: dts: exynos: enable PMIC wakeup from suspend on SMDK5420

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/20210420164943.11152-9-krzysztof.kozlowski@canonical.com

arch/arm/boot/dts/exynos5420-smdk5420.dts

@@ -132,6 +132,7 @@ &hsi2c_4 {
 	pmic@66 {
 		compatible = "samsung,s2mps11-pmic";
 		reg = <0x66>;
+		wakeup-source;
 
 		s2mps11_osc: clocks {
 			compatible = "samsung,s2mps11-clk";