spapr_drc: initial implementation of sPAPRDRConnector device

This device emulates a firmware abstraction used by pSeries guests to
manage hotplug/dynamic-reconfiguration of host-bridges, PCI devices,
memory, and CPUs. It is conceptually similar to an SHPC device,
complete with LED indicators to identify individual slots to physical
physical users and indicate when it is safe to remove a device. In
some cases it is also used to manage virtualized resources, such a
memory, CPUs, and physical-host bridges, which in the case of pSeries
guests are virtualized resources where the physical components are
managed by the host.

Guests communicate with these DR Connectors using RTAS calls,
generally by addressing the unique DRC index associated with a
particular connector for a particular resource. For introspection
purposes we expose this state initially as QOM properties, and
in subsequent patches will introduce the RTAS calls that make use of
it. This constitutes to the 'guest' interface.

On the QEMU side we provide an attach/detach interface to associate
or cleanup a DeviceState with a particular sPAPRDRConnector in
response to hotplug/unplug, respectively. This constitutes the
'physical' interface to the DR Connector.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
