perf inject: Keep a copy of kcore_dir

If the input perf.data has a kcore_dir, copy it into the output, since
at least the kallsyms in the kcore_dir will be useful to the output.

Example:

 Before:

  $ ls -lR perf.data-from-desktop
  perf.data-from-desktop:
  total 916
  -rw------- 1 user user 931756 May 19 09:55 data
  drwx------ 2 user user   4096 May 19 09:55 kcore_dir

  perf.data-from-desktop/kcore_dir:
  total 42952
  -r-------- 1 user user  7582467 May 19 09:55 kallsyms
  -r-------- 1 user user 36388864 May 19 09:55 kcore
  -r-------- 1 user user     4828 May 19 09:55 modules

  $ perf inject -i perf.data-from-desktop -o injected-perf.data

  $ ls -lR injected-perf.data
  -rw------- 1 user user 931320 May 20 15:08 injected-perf.data

 After:

  $ perf inject -i perf.data-from-desktop -o injected-perf.data

  $ ls -lR injected-perf.data
  injected-perf.data:
  total 916
  -rw------- 1 user user 931320 May 20 15:21 data
  drwx------ 2 user user   4096 May 20 15:21 kcore_dir

  injected-perf.data/kcore_dir:
  total 42952
  -r-------- 1 user user  7582467 May 20 15:21 kallsyms
  -r-------- 1 user user 36388864 May 20 15:21 kcore
  -r-------- 1 user user     4828 May 20 15:21 modules

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/20220520132404.25853-6-adrian.hunter@intel.com


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