boards: olimex_lora_stm32wl_devkit: enable MPU and HW stack protection

The random MPU faults experienced before were actually caused by a too
small system work queue stack for LoRaWAN in a custom application.

PR #52550 adds a compile-time check to avoid such issues in the future.

Signed-off-by: Martin Jäger <martin@libre.solar>