x86: actually merge <asm/alternative.h>

This actually merges <asm-x86/alternative_{32,64}.h> into
<asm-x86/alternative.h>.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>