x86/xen: Disable APIC PM for Xen PV guests

x86/xen: Disable APIC PM for Xen PV guests

Xen PV guests support only few APIC registers and writes to
unsupported registers result in WARN_ONs. Most APIC accesses in these
guests  have been eliminated; however, lapic_suspend/resume are still
called (on 32-bit kernels).

We can disable APIC power management in xen_smp_prepare_boot_cpu()
(which is called after APIC has been initialized).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>