The MIO interface being used by the Zynq design does not require VREF.
Can I use this as a general I/O like in SelectIO? How should I connect it?
The VREF pin is dedicated and cannot be used as general I/O. If unneeded, it should be left floating.
This has been added to the latest version of User Guide 933, Zynq-7000 PCB Design and Pin Planning Guide.