perf probe: Support argument name

Set given names to event arguments. The syntax is same as kprobe-tracer,
you can add 'NAME=' right before each argument.

e.g.
  ./perf probe vfs_read foo=file

 then, 'foo' is set to the argument name as below.

  ./perf probe -l
  probe:vfs_read       (on vfs_read@linux-2.6-tip/fs/read_write.c with foo)

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100412171653.3790.74624.stgit@localhost6.localdomain6>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>