spapr: initialize VSMT before initializing the IRQ backend

spapr: initialize VSMT before initializing the IRQ backend

We will need to use xics_max_server_number() to create the sPAPRXive
object modeling the interrupt controller of the machine which is
created before the CPUs.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
[dwg: Fix style nit]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>