rtc: isl12057: enable support for the standard "wakeup-source" property
Though the isl12057 rtc driver should and will continue to support the
legacy "isil,irq2-can-wakeup-machine" property to enable RTC as the
wakeup source, we need to add support for the new standard property
"wakeup-source".
This patch adds support for "wakeup-source" property in addition to the
existing "isil,irq2-can-wakeup-machine" property.