[arm][cortex-m4] Add hardware stack guard support

Enable RT_USING_HW_STACK_GUARD on Cortex-M4, which was previously only
available on Cortex-M7 and Cortex-M33.

Core porting (libcpu/arm/cortex-m4/):
- Add mpu.c/mpu.h/mputype.h aligned with the Cortex-M7 MPU layer. The only
  difference is the default memory type attribute: Cortex-M4 has no L1 cache,
  so the cacheability bits are reduced to three cases.
- Add rt_hw_stack_guard_init() to cpuport.c.
- Add missing #include <rtconfig.h> to context_gcc.S and invoke
  rt_hw_mpu_table_switch() in the PendSV context switch path.
- Update SConscript to exclude mpu.c when memory protection is disabled.

BSP reference (bsp/stm32/stm32f407-fk407m2-zgt6/):
- board.h: include rtthread.h and define NUM_STATIC_REGIONS.
- board.c: define static_regions[] marking the Flash region read-only,
  guarded by RT_USING_MEM_PROTECTION so it is not enabled by default.

0 files changed, 0 insertions, 0 deletions