x86_64: Remove serialize_cpu() inline

- It was redundant with sync_core()
- It was unused
- It was broken: no input arguments to cpuid; could fault randomly
  depending on eax contents.

Now it's gone.

[ tglx: arch/x86 adaptation ]
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/asm-x86/processor_64.h

@@ -389,11 +389,6 @@ static inline void prefetchw(void *x)
 
 #define cpu_relax()   rep_nop()
 
-static inline void serialize_cpu(void)
-{
-	__asm__ __volatile__ ("cpuid" : : : "ax", "bx", "cx", "dx");
-}
-
 static inline void __monitor(const void *eax, unsigned long ecx,
 		unsigned long edx)
 {