ARM: dts: exynos: enable PMIC wakeup from suspend on Odroid X/U3

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/20210420164943.11152-6-krzysztof.kozlowski@canonical.com