soc: stm32: Disable null pointer exception detection by default

Null pointer exception detection systematically triggers an
assert when program is run with debug mode on, which is currently
systematic when flashed using openocd runner.
Until this is fixed in openocd, make sure this detection is not
enabled by default (which is currently the case in zephyr tests).

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>

soc/arm/st_stm32/common/Kconfig.defconfig.series

@@ -17,6 +17,13 @@ config SYS_CLOCK_TICKS_PER_SEC
 	default 4096 if STM32_LPTIM_TIMER && STM32_LPTIM_CLOCK_LSE
 	default 4000 if STM32_LPTIM_TIMER && STM32_LPTIM_CLOCK_LSI
 
+# Disable null pointer exception detection by default as long as debug
+# mode is left active by west runners (openocd mainly)
+# cf https://github.com/zephyrproject-rtos/zephyr/issues/32984
+choice CORTEX_M_DEBUG_NULL_POINTER_EXCEPTION_DETECTION
+	default CORTEX_M_DEBUG_NULL_POINTER_EXCEPTION_DETECTION_NONE
+endchoice
+
 config CLOCK_CONTROL_STM32_CUBE
 	default y
 	depends on CLOCK_CONTROL