perf/x86: Add Silvermont (22nm Atom) support

Compared to old atom, Silvermont has offcore and has more events
that support PEBS.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1374138144-17278-2-git-send-email-zheng.z.yan@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>