x86: puts read and write cr8 into pv_cpu_ops

This patch adds room for read and write_cr8 functions back in
pv_cpu_ops struct

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>