This is a problem in the 12.2 software release and is to be resolved for 12.3.
Following are some example scripts where you can change the part as appropriate:
Implement.sh
################################################################
#-----------------------------------------------------------------------------
# Script to synthesize and implement the RTL provided for the IBERT core
#-----------------------------------------------------------------------------
#Exit on Error enabled.
set -o errexit
#Create results directory
mkdir results
cp ../../chipscope_ibert.ngc ./results
cd ./results
##-------------------------------Run ngdbuild---------------------------------------
echo 'Running ngdbuild'
ngdbuild -uc ../../example_design/chipscope_ibert_top.ucf -p xc6vcx75t-ff484-2 chipscope_ibert.ngc chipscope_ibert_top.ngd
#end run ngdbuild section
##-------------------------------Run map-------------------------------------------
echo 'Running map'
map -w -p xc6vcx75t-ff484-2 -o chipscope_ibert_top.map.ncd chipscope_ibert_top.ngd
##-------------------------------Run par-------------------------------------------
echo 'Running par'
par -w -ol high chipscope_ibert_top.map.ncd chipscope_ibert_top.ncd
##---------------------------Report par results-------------------------------------
echo 'Running design through bitgen'
bitgen -d -g GWE_cycle:Done -g GTS_cycle:Done -g DriveDone:Yes -g StartupClk:Cclk -w chipscope_ibert_top.ncd
##-------------------------------Trace Report---------------------------------------
###################################################################################
Implement.bat
###################################################################################
REM Clean results directory
REM Create results directory
REM Change current directory to results
ECHO WARNING: Removing existing results directory
RMDIR /S /Q results
MKDIR results
COPY ..\..\chipscope_ibert.ngc .\results\
cd .\results
REM Run ngdbuild
ECHO 'Running NGDBUILD'
ngdbuild -uc ..\..\example_design\chipscope_ibert_top.ucf -p xc6vcx75t-ff484-2 chipscope_ibert.ngc chipscope_ibert_top.ngd
REM end run ngdbuild section
REM Run map
ECHO 'Running MAP'
map -w -p xc6vcx75t-ff484-2 -o chipscope_ibert_top.map.ncd chipscope_ibert_top.ngd
REM Run par
ECHO 'Running PAR'
par -w -ol high chipscope_ibert_top.map.ncd chipscope_ibert_top.ncd
REM Report par results
ECHO 'Running design through BITGEN'
bitgen -d -g GWE_cycle:Done -g GTS_cycle:Done -g DriveDone:Yes -g StartupClk:Cclk -w chipscope_ibert_top.ncd
###################################################################################