perf list: Support long jevents descriptions

perf list: Support long jevents descriptions

Previously we were dropping the useful longer descriptions that some
events have in the event list completely. This patch makes them appear with
perf list.

Old perf list:

baclears:
  baclears.all
       [Counts the number of baclears]

vs new:

perf list -v:
...
baclears:
  baclears.all
       [The BACLEARS event counts the number of times the front end is
        resteered, mainly when the Branch Prediction Unit cannot provide
        a correct prediction and this is corrected by the Branch Address
        Calculator at the front end. The BACLEARS.ANY event counts the
        number of baclears for any type of branch]

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1473978296-20712-13-git-send-email-sukadev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>