Calculate the virtulachain-required opfields dict.

def make_opfields( cls ):
        """
        Calculate the virtulachain-required opfields dict.
        """
        # construct fields 
        opfields = {}
        for opname in SERIALIZE_FIELDS.keys():
            opcode = NAME_OPCODES[opname]
            opfields[opcode] = SERIALIZE_FIELDS[opname]

        return opfields