Currently iMPACT does not support S25FL128S SPI Flash. However S25FL128P part appears in iMPACT when you set the following environment variable:
XIL_IMPACT_SPI_SPANSION_S25FL_QJYPT = 1
You are able to program toS25FL128S SPI Flashby selectingS25FL128P part. It's only 64 Kb sector size only.
For 256Kb sector size, it's planning in 14.1, but not yet fixed.