x86: move load_cr3 to a common place.

There are currently two definitions of load_cr3, that essentially do the
same thing. This patch moves them all to processor.h.

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>