perf trace beauty: Give syscall return beautifier more context

We need the current thread and the trace internal state so that we can
use the fd beautifier to augment syscall returns, so use struct
syscall_arg with some fields that make sense on returns (val, thread,
trace).

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-lqag8e86ybidrh5zpqne05ov@git.kernel.org


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