gpgscm: Move files to a gpgscm subdirectory.

Note that we used

git filter-branch --subdirectory-filter tests/gpgscm

in gnupg master to filter out the gpgscm part. This commit merely
moves these files to a subdirectory which will be used in libgpg-error
for gpgscm.

• Signed-off-by: Werner Koch <wk@gnupg.org>