perf auxtrace: Factor out itrace_do_parse_synth_opts()

Factor out itrace_do_parse_synth_opts() so that it can be reused.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210530192308.7382-9-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>