sched/cpuacct: Add cpuacct_init()

So we don't open-coded initialization of cpuacct in core.c.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51553687.1060906@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --cc kernel/sched/core.c
Simple merge

diff --cc kernel/sched/cpuacct.c
Simple merge

diff --cc kernel/sched/cpuacct.h
Simple merge