perf tools: Allow the specification of all tracepoints at once

Currently, when one wants to activate every tracepoint
counters of a subsystem from perf record, the current sequence
is needed:

  perf record -e subsys:ev1 -e subsys:ev2 -e subsys:ev3

This may annoy the most patient of us.

Now we can just do:

  perf record -e subsys:*

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>