Hi,
57xx_flash.ld is linker file. There is no .lcf file in S32 Design Studio. Instead of it, suffix .ld is used.
When you create multi-core project, linker file for multi-core is generated and it does not matter, which core you are using now.
When you create single project only (uncheck the z7 cores buttons in project wizard during creating project), you will have following linker file in your project.

If you have any other questions, please feel free to write me back.
Regards,
Martin