ppc/pnv: add a PSI bridge model for POWER9

ppc/pnv: add a PSI bridge model for POWER9

The PSI bridge on POWER9 is very similar to POWER8. The BAR is still
set through XSCOM but the controls are now entirely done with MMIOs.
More interrupts are defined and the interrupt controller interface has
changed to XIVE. The POWER9 model is a first example of the usage of
the notify() handler of the XiveNotifier interface, linking the PSI
XiveSource to its owning device model.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20190307223548.20516-3-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>