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 s390x-specific values

CT_DoArchTupleValues() {

    # The kernel architecture is the same name as for the 32-bit version:

    CT_KERNEL_ARCH="s390"

}