spapr/xive: introduce a XIVE interrupt controller

spapr/xive: introduce a XIVE interrupt controller

sPAPRXive models the XIVE interrupt controller of the sPAPR machine.
It inherits from the XiveRouter and provisions storage for the routing
tables :

  - Event Assignment Structure (EAS)
  - Event Notification Descriptor (END)

The sPAPRXive model incorporates an internal XiveSource for the IPIs
and for the interrupts of the virtual devices of the guest. This model
is consistent with XIVE architecture which also incorporates an
internal IVSE for IPIs and accelerator interrupts in the IVRE
sub-engine.

The sPAPRXive model exports two memory regions, one for the ESB
trigger and management pages used to control the sources and one for
the TIMA pages. They are mapped by default at the addresses found on
chip 0 of a baremetal system. This is also consistent with the XIVE
architecture which defines a Virtualization Controller BAR for the
internal IVSE ESB pages and a Thread Managment BAR for the TIMA.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
[dwg: Fold in field accessor fixes]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>