dt-bindings: lito-pinctrl: add wakeup interrupt parent for GPIO

Lito SoC has an always-on interrupt controller (PDC) with select GPIO
routed to the PDC as interrupts that can be used to wake the system up
from deep low power modes and suspend.

Change-Id: If187d34c0f296bd087ed04eca8240681469c548b
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>