powerpc/pseries: Correct pseries/dlpar.c build break without CONFIG_SMP

The recent patch to add cpu offline/online as part of the DLPAR
process for pseries causes a build break if CONFIG_SMP is not
defined.  Original patch here;
http://lists.ozlabs.org/pipermail/linuxppc-dev/2009-November/078299.html

This corrects the build break by moving the online_node_cpus
and offline_node_cpus under the #ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
portions of dlpar.c.

This patch also slightly modifies the online_node_cpus and offline_node_cpus
routines to prepend dlpar_ to the them and make them static.  These two
routine are only used in the dlpar add/remove of cpus and these changes
should help clarify that.

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