[nrf noup] soc: Use DWT for null-pointer detection on nRF5340 net core

squash! [nrf noup] soc: nrf: Switch null-pointer detection option to MPU

The MPU-based null-pointer dereference detection cannot be used on
the network core in nRF5340 because of its flash base address and
this causes the zephyr/tests/arch/arm/arm_interrupt test to fail.
Use the DWT option instead for this core.

Ref. NCSDK-11348

Signed-off-by: Andrzej Głąbek <[email protected]>

Author: anangl

soc/arm/nordic_nrf/Kconfig.defconfig

@@ -43,8 +43,10 @@ config GPIO
 	depends on SPI
 
 # Switch the default mechanism for null-pointer dereference detection from
-# DWT-based to MPU-based.
+# DWT-based to MPU-based, except for the network core on nRF5340 where the
+# MPU-based mechanism cannot be used.
 choice NULL_POINTER_EXCEPTION_DETECTION
+	default NULL_POINTER_EXCEPTION_DETECTION_DWT if SOC_NRF5340_CPUNET
 	default NULL_POINTER_EXCEPTION_DETECTION_MPU if TEST_ARM_CORTEX_M && !ARM_NONSECURE_FIRMWARE
 endchoice