gpio: nxp_s32: support passing external interrupts to WKPU

Extend the NXP S32 GPIO driver to be able to route external interrupts
to either SIUL2 EIRQ interrupt controller or, when available on the
SoC, WKPU interrupt controller.

Since WKPU can support up to 64 external interrupt sources and SIUL2
EIRQ up to 32, gpio_get_pending_int() is removed and the interrupt
controller specific API must be used instead.

Signed-off-by: Manuel Argüelles <manuel.arguelles@nxp.com>