The XDC targets the KC705 when either the correct Kintex 7 FPGA part (XC7K325TFFG900) is selected, or when the KC705 board is targeted directly in the Vivado project options.
Figure 1. KC705 Board Connectivity
The XDC targets the KC705 when either the correct Kintex 7 FPGA part (XC7K325TFFG900) is selected, or when the KC705 board is targeted directly in the Vivado project options.