perf: offcore event monitoring patches

Hi,

Here is the updated offcore patches. I merged small changes and fixes into the first patch, see the change logs.

Change logs against Andi's original version:
- Extends perf_event_attr:config to config{,1,2} (Peter Zijlstra)
- Fixed a major event scheduling issue. There cannot be a ref++ on an event that has already done ref++ once and without calling put_constraint() in between. (Stephane Eranian)
- Use thread_cpumask for percore allocation. (Lin Ming)
- Use MSR names in the extra reg lists. (Lin Ming)

Peter,
The event scheduling issue was fixed, could you please consider merging this series?

Thanks,
Lin Ming