perf data: Add has_kcore_dir()

Add a helper function has_kcore_dir(), so that perf inject can determine if
it needs to keep the kcore_dir.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220520132404.25853-5-adrian.hunter@intel.com


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