spapr/xive: use SPAPR_IRQ_IPI to define IPI ranges exposed to the guest

spapr/xive: use SPAPR_IRQ_IPI to define IPI ranges exposed to the guest

The "ibm,xive-lisn-ranges" defines ranges of interrupt numbers that
the guest can use to configure IPIs. It starts at 0 today but it could
change to some other offset. Make clear which IRQ range we are
exposing by using SPAPR_IRQ_IPI in the property definition.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20200306123307.1348-1-clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>