gpg: Allow building with older libgpg-error.

* g10/mainproc.c (proc_encrypted): Use constant from logging.h

Because the log levels are enums I had to change there names in
libgpg-error to avoid clashes. Master uses the new names but 2.2
needs to stick to the old names.

• Fixes-commit: 825909e9cd5f344ece6c0b0ea3a9475df1d643de
• Signed-off-by: Werner Koch <wk@gnupg.org>