Only allocate per CPU data for possible CPUs.

Saves some memory.

Requires earlier patch to set up possible map earlier

Index: linux/arch/x86_64/kernel/setup64.c
===================================================================
--- linux.orig/arch/x86_64/kernel/setup64.c
+++ linux/arch/x86_64/kernel/setup64.c
@@ -99,9 +99,8 @@ void __init setup_per_cpu_areas(void)
 		size = PERCPU_ENOUGH_ROOM;
 #endif
 
-	for (i = 0; i < NR_CPUS; i++) { 
+	for_each_cpu_mask(i, cpu_possible_map) { 
 		unsigned char *ptr;
-
 		if (!NODE_DATA(cpu_to_node(i))) {
 			printk("cpu with no node %d, num_online_nodes %d\n",
 			       i, num_online_nodes());