Adding scanner/parser bits to parse event groups.

The grammar for group is:
  groups:      groups ',' group | group
  group:       group_name '{' events '}' group_mod
  group_name:  name | empty
  group_mod:   ':' group_mods | empty
  group_mods:  event_mod

It's possible to use standard event modifier as a modifier
for group. It'll be used as an update to existing event
modifiers.

It's necessary to use quoting ("'\) when specifying group on
command line, since {} characters are interpreted by most of
the shells.

It is now possible to specify groups in event syntax like:

  '{cycles,faults}'
   - anonymous group

  'group1{cycles,faults}
   - group with name 'group1'

  '{cycles,faults}:k
   - anonymous group with event modifier 'k'

  '{cpu-clock,task-clock},{minor-faults,major-faults}'
   - two anonymous groups

The grouping functionality itself is coming shortly.
Reviewed-by: NNamhyung Kim <namhyung@kernel.org>
Signed-off-by: NJiri Olsa <jolsa@redhat.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ulrich Drepper <drepper@gmail.com>
Link: http://lkml.kernel.org/n/tip-p4j8bnvo879uokum4k4zk5q6@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>