scripts: add "FILE" and "CFG" debug levels.

I ran into some minor difficulties looking through the build log for a
particular file: I wasn't interested in seeing it unpacked, but only
when it is built or installed. Adding these two levels allows me to
differentiate between those cases.

[Yann E. MORIN: Those are blind log levels, and are used only to search
in the build-log afterward.]

Signed-off-by: Anthony Foiani <anthony.foiani@gmail.com>

 # Compute s390-specific values

 CT_DoArchTupleValues() {

     # That's the only thing to override

     if [ "${CT_ARCH_64}" = "y" ]; then

         CT_TARGET_ARCH="s390x"

     fi

 }