perf/tool: Add PMU event alias support

Add support to specify alias term within the event description.

The definition of pmu event alias is located at:

  ${sysfs_mount}/bus/event_source/devices/${pmu}/events/

Each file in the 'events' directory defines a event alias. Its contents
are like:

  config=1,config1=2

Using pmu event alias, an event can be now specified like:

  uncore/CLOCKTICKS/ or uncore/event=CLOCKTICKS/

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
[ Cleaned it up. ]
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1339741902-8449-13-git-send-email-zheng.z.yan@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>