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

The RTC on Maxim max77686 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/20210420164943.11152-5-krzysztof.kozlowski@canonical.com

arch/arm/boot/dts/exynos4412-midas.dtsi

@@ -668,6 +668,7 @@ max77686: pmic@9 {
 		interrupts = <7 IRQ_TYPE_LEVEL_LOW>;
 		pinctrl-0 = <&max77686_irq>;
 		pinctrl-names = "default";
+		wakeup-source;
 		reg = <0x09>;
 		#clock-cells = <1>;