tools lib traceevent: Factor out allocating and processing args

The sequence of allocating the print_arg field, calling process_arg()
and verifying that the next event delimiter is repeated twice in
process_hex() and will also be used for process_int_array().

Factor it out to a function to avoid writing the same code again and
again.

Signed-off-by: Javi Merino <javi.merino@arm.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1426875176-30244-2-git-send-email-javi.merino@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>