powerpc/pseries: Expose pseries devicetree_update()

Newer firmware on Power systems can transparently reassign platform resources
(CPU and Memory) in use. For instance, if a processor or memory unit is
predicted to fail, the platform may transparently move the processing to an
equivalent unused processor or the memory state to an equivalent unused
memory unit. However, reassigning resources across NUMA boundaries may alter
the performance of the partition. When such reassignment is necessary, the
Platform Resource Reassignment Notification (PRRN) option provides a
mechanism to inform the Linux kernel of changes to the NUMA affinity of
its platform resources.

When rtasd receives a PRRN event, it needs to make a series of RTAS
calls (ibm,update-nodes and ibm,update-properties) to retrieve the
updated device tree information. These calls are already handled in the
pseries_devicetree_update() routine used in partition migration.

This patch exposes pseries_devicetree_update() to make it accessible
to other pseries routines, this patch also updates pseries_devicetree_update()
to take a 32-bit scope parameter. The scope value, which was previously hard
coded to 1 for partition migration, is used for the RTAS calls
ibm,update-nodes/properties to update the device tree.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>