x86: unify msr smp funcs

The functions under #ifdef CONFIG_SMP in msr.h are the same
for both x86_64 and i386, and this patches removes one of them,
putting them in a single location

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>