arch/s390: cleanups

Don't select unneeded config knobs. Don't select non-existing config knobs.
Use the "no patch" config knob, instead of pointing to an non-exiting local
patch dir. Simplify the tuple-related scripts. Update the samples.

# Compute x86_64-specific values

CT_DoArchTupleValues() {

    # The architecture part of the tuple:

    CT_TARGET_ARCH="${CT_ARCH}"

}