perf script: Refine printing of dso offset (dsoff)

Print dso offset only for object files, and in those cases force using the
dso->long_name if the dso->name starts with '[' or the dso is kcore, in
order to avoid special names such as [vdso], or mixing up kcore with
vmlinux.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Changbin Du <changbin.du@huawei.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20230424055107.12105-3-adrian.hunter@intel.com


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