csky: Fixup pmu probe failed

We can't directly use CPUHP_AP_PERF_ONLINE as cpuhp_setup_state,
it will cause return -EBUSY. Define CPUHP_AP_PERF_CSKY_ONLINE just
as X86's will solve the problem.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Tested-by: Chen Pei <hanyu.cp@alibaba-inc.com>
Reported-by: Xiang Yuanchao <xiangzhi.xyc@alibaba-inc.com>