include: zephyr: drivers: gpio: Propagate GPIO_INT_WAKEUP flag

The GPIO_INT_WAKEUP flag is available in the binding header,
but was not propagated from dt_flags in the interrupt_configure_dt
function. Allow GPIOs to be declared as wakeup sources in dts
by propagating the flag.

Signed-off-by: Aksel Skauge Mellbye <aksel.mellbye@silabs.com>