drivers: gpio: nrfx: Add support for GPIOTE0 on cpurad

Add support for special GPIOTE0 instance on nrf54h20/cpurad.
This instance requires special handling because:
- there is no support for PORT event (level interrupts)
- TE channels are fixed to the pin

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>