ppc/xive: Introduce a XiveFabric interface

ppc/xive: Introduce a XiveFabric interface

The XiveFabric QOM interface acts as the PowerBUS interface between
the interrupt controller and the system and should be implemented by
the QEMU machine. On HW, the XIVE sub-engine is responsible for the
communication with the other chip is the Common Queue (CQ) bridge
unit.

This interface offers a 'match_nvt' handler to perform the CAM line
matching when looking for a XIVE Presenter with a dispatched NVT.

Reviewed-by: Greg Kurz <[email protected]>
Signed-off-by: Cédric Le Goater <[email protected]>
Message-Id: <20191125065820[email protected]>
Signed-off-by: David Gibson <[email protected]>