I don't think it is possible with FX3. You can provide a clock from the GPIF II interface to the image sensor. But then that interface runs at that particular clock only.
We don’t have that facility on FX3 to provide a clock to the external peripheral and let GPIF II interface work on different clock.
But our USB 2.0 controller (FX2LP) can do that. This is documented in the following application note:
Please look for “CLKOUT” in that application note.