feat: arm64: update thread self on sp-switch

This patch improves the atomicity of context switching by ensuring that
the stack pointer (sp) and thread self updates occur simultaneously.
This enhancement is crucial for maintaining thread safety and
preventing potential inconsistencies during context switches.

Changes:
- Modified `cpuport.h` to use `ARM64_THREAD_REG` for thread self access.
- Added an `update_tidr` macro in `context_gcc.S` to streamline thread ID
  updates.
- Adjusted `rt_hw_context_switch_to` and `rt_hw_context_switch` to call
  `update_tidr`, ensuring atomic updates during context switches.
- Cleaned up `scheduler_mp.c` by removing redundant thread self
  assignments.

Signed-off-by: Shell <smokewood@qq.com>

src/scheduler_mp.c

@@ -1069,9 +1069,6 @@ void rt_sched_post_ctx_switch(struct rt_thread *thread)
     }
     /* safe to access since irq is masked out */
     pcpu->current_thread = thread;
-#ifdef ARCH_USING_HW_THREAD_SELF
-    rt_hw_thread_set_self(thread);
-#endif /* ARCH_USING_HW_THREAD_SELF */
 }
 
 #ifdef RT_DEBUGING_CRITICAL