powerpc/numa: Increase SD_NODES_PER_DOMAIN to 32.

The largest POWER7 boxes have 32 nodes. SD_NODES_PER_DOMAIN groups
nodes into chunks of 16 and adds a global balancing domain
(SD_ALLNODES) above it.

If we bump SD_NODES_PER_DOMAIN to 32, then we avoid this extra
level of balancing on our largest boxes.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/topology.h

@@ -28,6 +28,12 @@ struct device_node;
  */
 #define RECLAIM_DISTANCE 10
 
+/*
+ * Avoid creating an extra level of balancing (SD_ALLNODES) on the largest
+ * POWER7 boxes which have a maximum of 32 nodes.
+ */
+#define SD_NODES_PER_DOMAIN 32
+
 #include <asm/mmzone.h>
 
 static inline int cpu_to_node(int cpu)