cptofs: allow to override owner/group when copying files

[Mic92]

cptofs is useful to write images without using virtual machines or having root access. This option allows to also write content as a different owner/group.

[tavip]

LGTM, thanks @Mic92 !

[tavip]

@Mic92 sorry for catching this late, there are a few coding style issues.

[Mic92]

Should be fine now:

$ scripts/checkpatch.pl tools/lkl/cptofs.c
WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
#1: FILE: tools/lkl/cptofs.c:1:
+#ifdef __FreeBSD__

total: 0 errors, 1 warnings, 693 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

tools/lkl/cptofs.c has style problems, please review.

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.