perf kmem: Collect cross node allocation statistics

Show cross node memory allocations:

 # ./perf kmem

 SUMMARY
 =======
 ...
 Cross node allocations: 0/3633

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-mm@kvack.org <linux-mm@kvack.org>
LKML-Reference: <4B0B6E87.10906@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>