xen/x86: Call xen_smp_intr_init_pv() on BSP

Recent code rework that split handling ov PV, HVM and PVH guests into
separate files missed calling xen_smp_intr_init_pv() on CPU0.

Add this call.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Juergen Gross <jgross@suse.com>