xics_spapr and xics_kvm nearly define the same 'set_nr_servers'
handler. Only the type of the ICP differs. So let's make a common one
to remove some duplicated code.
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>