kvm/i386: Add xen-evtchn-max-pirq property

The default number of PIRQs is set to 256 to avoid issues with 32-bit MSI
devices. Allow it to be increased if the user desires.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

accel/kvm/kvm-all.c

@@ -3705,6 +3705,7 @@ static void kvm_accel_instance_init(Object *obj)
     s->notify_window = 0;
     s->xen_version = 0;
     s->xen_gnttab_max_frames = 64;
+    s->xen_evtchn_max_pirq = 256;
 }
 
 /**