spapr, xics, xive: Move set_irq from SpaprIrq to SpaprInterruptController

spapr, xics, xive: Move set_irq from SpaprIrq to SpaprInterruptController

This method depends only on the active irq controller.  Now that we've
formalized the notion of active controller we can dispatch directly through
that, rather than dispatching via SpaprIrq with the dual version having
to do a second conditional dispatch.

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>