fmcomms1: Changed ILA data capture and sys constraints

The ILA can not work at 250MHz on ZED/ZC702. Because of this, the data
path was modified from 28bits@250MHz to 56bits@125MHz, by using a FIFO.
The ZED/ZC702 max BUFG frequency is 464MHz, which corresponds to a 2.16
period so the constraints were modified accordingly.