cpuid is not very different between i386 and x86_64.
We move away the x86_64 version from msr.h, and
unify them at processor.h, where they belong.

cpuid() paravirt then comes for free.
Signed-off-by: NGlauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>