Fix IBUFDS_GTE to GTP_COMMON connection

[acomodi]

Each GTP_COMMON in the Series7 has two different IBUFDS_GTE from which it can get the differential clock signals. The GTP_COMMON itself has two GTREFCLK inputs, each of them exclusively connected to one of the IBUFDS_GTE.

Using Vivado, having the connection from an IBUFDS_GTE to a "physically unconnected" GTREFCLK input is still allowed as the tool apparently rearranges the netlist. This isn't the case in Yosys+VTR, where, the connection will not be present.

[lgl1227]

This issue is still open. Has this connection problem not been fixed yet?