powerpc/pseries: Use kernel hotplug queue for PowerVM hotplug events

The sysfs interface used to handle PowerVM hotplug events should use the
hotplug queue as well. PRRN events will soon be placing many hotplug
events on the queue at once and we will need ordinary hotplug events to
use the queue as well in order to ensure these events will still be handled
and that proper serialization is maintained during the PRRN event.

Signed-off-by: John Allen <jallen@linux.vnet.ibm.com>
Reviewed-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>