x86: move nop declarations into separate include file

Moving things out of processor.h is always a good thing.

Also needed to avoid include loop in later patch.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>