x86: move the definition of set_iopl_mask to common header

This patch moves the definition of set_iopl_mask to processor.h,
instead of letting it at processor_32.h.
For x86_64, nothing is done, as we don't really need such a function.
However, having it on both arches saves us from putting an ifdef in the
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>