if you want to make it bidirectional for I/O... with a FET... i don't remember ... but is well documented on I2C Phillips standard: connect FPGA lines to source, DSP lines to drain and the lower voltaje to the gate, don't trust me at all, verify first.
actually i was thinking of connecting them using ethernet.. but it's said the the FPGA has only ethernet PHY but i dunno why would they do PHY without the support of the MAC layer !!!