config/arch: re-organise architecture-specific options

Move the arch-specific options to the second-part of
the generated files, so they appear after the generic
options, but before the optimisations.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Compute s390-specific values

 CT_DoArchTupleValues() {

     # That's the only thing to override

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

         CT_TARGET_ARCH="s390x"

     fi

 }