[POWERPC] fix building without PCI

At least the ide driver calls pcibus_to_node, which is not
defined when CONFIG_PCI is disabled. This adds a nop function
for the !PCI case.
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

include/asm-powerpc/topology.h

@@ -32,7 +32,14 @@ static inline int node_to_first_cpu(int node)
 int of_node_to_nid(struct device_node *device);
 
 struct pci_bus;
+#ifdef CONFIG_PCI
 extern int pcibus_to_node(struct pci_bus *bus);
+#else
+static inline int pcibus_to_node(struct pci_bus *bus)
+{
+	return -1;
+}
+#endif
 
 #define pcibus_to_cpumask(bus)	(pcibus_to_node(bus) == -1 ? \
 					CPU_MASK_ALL : \