spapr: Remove SpaprIrq::init_kvm hook

spapr: Remove SpaprIrq::init_kvm hook

This hook is a bit odd.  The only caller is spapr_irq_init_kvm(), but
it explicitly takes an SpaprIrq *, so it's never really called through the
current SpaprIrq.  Essentially this is just a way of passing through a
function pointer so that spapr_irq_init_kvm() can handle some
configuration and error handling logic without duplicating it between the
xics and xive reset paths.

So, make it just take that function pointer.  Because of earlier reworks
to the KVM connect/disconnect code in the xics and xive backends we can
also eliminate some wrapper functions and streamline error handling a bit.

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