spapr_pci: enable basic hotplug operations

This enables hotplug for PHB bridges. Upon hotplug we generate the
OF-nodes required by PAPR specification and IEEE 1275-1994
"PCI Bus Binding to Open Firmware" for the device.

We associate the corresponding FDT for these nodes with the DrcEntry
corresponding to the slot, which will be fetched via
ibm,configure-connector RTAS calls by the guest as described by PAPR
specification. The FDT is cleaned up in the case of unplug.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
spapr_events: re-use EPOW event infrastructure for hotplug events

This extends the data structures currently used to report EPOW events to
gets via the check-exception RTAS interfaces to also include event types
for hotplug/unplug events.

This is currently undocumented and being finalized for inclusion in PAPR
specification, but we implement this here as an extension for guest
userspace tools to implement (existing guest kernels simply log these
events via a sysfs interface that's read by rtas_errd).

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
spapr_events: event-scan RTAS interface

We don't actually rely on this interface to surface hotplug events, and
instead rely on the similar-but-interrupt-driven check-exception RTAS
interface used for EPOW events. However, the existence of this interface
is needed to ensure guest kernels initialize the event-reporting
interfaces which will in turn be used by userspace tools to handle these
events, so we implement this interface as a stub.

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
spapr_pci: emit hotplug add/remove events during hotplug

This uses extension of existing EPOW interrupt/event mechanism
to notify userspace tools like librtas/drmgr to handle
in-guest configuration/cleanup operations in response to
device_add/device_del.

Userspace tools that don't implement this extension will need
to be run manually in response/advance of device_add/device_del,
respectively.

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
*fixup for enable hp