arch/arm64: fix backtrace register access and gdbstub config guard

Fix arm64_backtrace to access TCB register context directly instead of using
running_regs(), which may not reflect the actual context being backtraced.
Add CONFIG_ARCH_HAVE_DEBUG guard to prevent undefined references in non-debug builds.

Signed-off-by: hujun5 <hujun5@xiaomi.com>

arch/arm64/src/common/arm64_backtrace.c

@@ -162,8 +162,8 @@ int up_backtrace(struct tcb_s *tcb,
     {
       ret = backtrace(tcb->stack_base_ptr,
                       tcb->stack_base_ptr + tcb->adj_stack_size,
-                      running_regs()[REG_X29],
-                      running_regs()[REG_ELR],
+                      (void *)(tcb->xcp.regs)[REG_X29],
+                      (void *)(tcb->xcp.regs)[REG_ELR],
                       buffer, size, &skip);
     }
 

libs/libc/gdbstub/lib_gdbstub.c

@@ -116,7 +116,7 @@ static const struct memory_region_s g_memory_region[] =
 };
 #endif
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) && defined(CONFIG_ARCH_HAVE_DEBUG)
 static struct smp_call_data_s g_call_data;
 #endif