perf tools: Accept case-insensitive symbolic event variants

We currently fail on something like '-e CPU-migrations', with:

  invalid or unsupported event: 'CPU-migrations'

While 'CPU-migrations' is how we actually print out the event
in the default perf stat output:

 Performance counter stats for 'true':

          0.202204 task-clock-msecs         #      0.282 CPUs
                 0 context-switches         #      0.000 M/sec
                 0 CPU-migrations           #      0.000 M/sec

So change the matching to be case-insensitive.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/n/tip-omcm3edjjtx83a4kh2e244se@git.kernel.org


Signed-off-by: Ingo Molnar <mingo@elte.hu>