[IA64] Fix undefined reference to can_cpei_retarget for simulator

The simulator build doesn't turn on ACPI, so doesn't have a definition
of can_cpei_retarget.
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/topology.c

@@ -36,12 +36,14 @@ int arch_register_cpu(int num)
 	parent = &sysfs_nodes[cpu_to_node(num)];
 #endif /* CONFIG_NUMA */
 
+#ifdef CONFIG_ACPI_BOOT
 	/*
 	 * If CPEI cannot be re-targetted, and this is
 	 * CPEI target, then dont create the control file
 	 */
 	if (!can_cpei_retarget() && is_cpu_cpei_target(num))
 		sysfs_cpus[num].cpu.no_control = 1;
+#endif
 
 	return register_cpu(&sysfs_cpus[num].cpu, num, parent);
 }