arch: rename the SUPPORT_XXX options

First, 'SUPPORT' should be spelled 'SUPPORTS'.

Second, 'SUPPORT_XXX' really means 'supports --with-xxx', so rename the
affected options accordingly. Update the affected archs to match the new
namings.

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
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

}