spapr_rtas: add ibm, configure-connector RTAS interface

spapr_rtas: add ibm, configure-connector RTAS interface

This interface is used to fetch an OF device-tree nodes that describes a
newly-attached device to guest. It is called multiple times to walk the
device-tree node and fetch individual properties into a 'workarea'/buffer
provided by the guest.

The device-tree is generated by QEMU and passed to an sPAPRDRConnector during
the initial hotplug operation, and the state of these RTAS calls is tracked by
the sPAPRDRConnector. When the last of these properties is successfully
fetched, we report as special return value to the guest and transition
the device to a 'configured' state on the QEMU/DRC side.

See docs/specs/ppc-spapr-hotplug.txt for a complete description of
this interface.

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