x86: put together equal pieces of system.h

This patch puts together pieces of system_{32,64}.h that
looks like the same. It's the first step towards integration
of this file.

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>