powerpc/pseries: Introduce memory hotplug READD operation

powerpc/pseries: Introduce memory hotplug READD operation

BugLink: http://bugs.launchpad.net/bugs/1670315
Currently, memory must be hot removed and subsequently re-added in order
to dynamically update the affinity of LMBs specified by a PRRN event.
Earlier implementations of the PRRN event handler ran into issues in which
the hot remove would occur successfully, but a hotplug event would be
initiated from another source and grab the hotplug lock preventing the hot
add from occurring. To prevent this situation, this patch introduces the
notion of a hot "readd" action for memory which atomizes a hot remove and
a hot add into a single, serialized operation on the hotplug queue.

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>
(cherry picked from commit e70d59700fc32c9249b26acd4120303c497e84f1)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>