CPU: Add a pause() method

kernel/src/arch/CPU.h

@@ -25,4 +25,6 @@ namespace CPU
     void print_stack_trace();
     void get_stack_trace_at(Registers* regs, void (*callback)(u64, void*), void* arg);
     void print_stack_trace_at(Registers* regs);
+
+    void pause();
 }

kernel/src/arch/x86_64/CPU.cpp

@@ -506,6 +506,11 @@ namespace CPU
             },
             &frame_index);
     }
+
+    void pause()
+    {
+        asm volatile("pause");
+    }
 }
 
 // called by kernel_yield