Differential clock input on ZedBoard
I don't know that particular board, but there is more then you ever want to know about the clocking on the 7 series parts here:

http://www.xilinx.com/support/documentation/user_guides/ug472_7Series_Clocking.pdf

Basically you can run a single ended clock into the thing (Subject to picking an appropriate IO standard), but there are constraints to watch out for if you wish to clock multiple regions from one input. 
Single ended clocks (Not usually a good idea at high speed!) must go in on the positive half of the pair (You can use the negative pin as a general IO pin if using a single ended IO standard).

For a global clock you want a pin with MRCC (Multi region clock capable) in the name Vivado pin planner is useful here for figuring out what can do what. 

73