Wrong value for PLATFORM_REPO_PATHS in 15 README.md files

[ThomasGmeinder]

There are 15 README.md files which suggest this: Set up your PLATFORM_REPO_PATHS environment variable to $XILINX_VITIS/lin64/Vitis/2024.1/base_platforms/.

The value $XILINX_VITIS/lin64/Vitis/2024.1/base_platforms/ is wronge in Vitis 2024.1.

The correct path is: $XILINX_VITIS/base_platforms/

[xflorentw]

I believe it is not even required to set PLATFORM_REPO_PATHS to $XILINX_VITIS/base_platforms/. Vitis will check into $XILINX_VITIS/base_platforms/ in any case but the makefiles have to be modified to point to the platform name and not to the .xpfm file