metag: topology: export 'cpu_core_map'

We need to export 'cpu_core_map' since the topology_core_cpumask macro
refers to it and is used by certain kernel modules.

Found in allmodconfig build:
ERROR: "cpu_core_map" [drivers/staging/lustre/lustre/libcfs/libcfs.ko] undefined!

Signed-off-by: Chen Gang <[e-mail]>
Signed-off-by: James Hogan <[e-mail]>

arch/metag/kernel/topology.c

···
 DEFINE_PER_CPU(struct cpuinfo_metag, cpu_data);
 
 cpumask_t cpu_core_map[NR_CPUS];
+EXPORT_SYMBOL(cpu_core_map);
 
 static cpumask_t cpu_coregroup_map(unsigned int cpu)
 {