soc: nordic_nrf: Add Kconfig options for APPROTECT handling

Add Kconfig options that allow users to select the way the APPROTECT
mechanism is handled in the SystemInit() function.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>