When you generate an RLDRAM II controller using Nios II-based sequencer, the MegaWizard™ will generate the top level IP module with the 2-bit wide signal
This signal serves no functional purpose but is needed to allow the dk pins to be assigned to a DQ group. In the Nios II-based sequencer instantiation, the dk pins must exist in a DQ group in order to access hardware required for calibration.
You need to bring the
signal up to the top level and connect it to a DQ pin in a x4 DQS group but there is no need to connect it to anything external to the FPGA as these pins serve no purpose.