These dev boards have provision for users to implement PWM contorl of the cooling fan but I've not found any IP blocks. This seems like something someone should have done before but perhaps I'm wrong.
Is there a thermometer in the Ultrascale devices that a user can read in order to set the fan speed?
So it seems Google is better at searching than Xilinx own documentation. :-)
UG580 was what I was looking for.