powerpc/pseries: Fix build break for SPLPAR=n and CPU hotplug

Commit e67e02a ("powerpc/pseries: Fix cpu hotplug crash with
memoryless nodes") adds an unconditional call to
find_and_online_cpu_nid(), which is only declared if CONFIG_PPC_SPLPAR
is enabled. This results in the following build error if this is not
the case.

  arch/powerpc/platforms/pseries/hotplug-cpu.o: In function `dlpar_online_cpu':
  arch/powerpc/platforms/pseries/hotplug-cpu.c:369:
  			undefined reference to `.find_and_online_cpu_nid'

Follow the guideline provided by similar functions and provide a dummy
function if CONFIG_PPC_SPLPAR is not enabled. This also moves the
external function declaration into an include file where it should be.

Fixes: e67e02a ("powerpc/pseries: Fix cpu hotplug crash with memoryless nodes")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
[mpe: Change subject to emphasise the build fix]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/topology.h

@@ -87,6 +87,7 @@ static inline int numa_update_cpu_topology(bool cpus_locked)
 extern int start_topology_update(void);
 extern int stop_topology_update(void);
 extern int prrn_is_enabled(void);
+extern int find_and_online_cpu_nid(int cpu);
 #else
 static inline int start_topology_update(void)
 {
@@ -100,6 +101,10 @@ static inline int prrn_is_enabled(void)
 {
 	return 0;
 }
+static inline int find_and_online_cpu_nid(int cpu)
+{
+	return 0;
+}
 #endif /* CONFIG_NUMA && CONFIG_PPC_SPLPAR */
 
 #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_NEED_MULTIPLE_NODES)

arch/powerpc/platforms/pseries/hotplug-cpu.c

@@ -342,8 +342,6 @@ static void pseries_remove_processor(struct device_node *np)
 	cpu_maps_update_done();
 }
 
-extern int find_and_online_cpu_nid(int cpu);
-
 static int dlpar_online_cpu(struct device_node *dn)
 {
 	int rc = 0;