update fwk Vitis integration

Some changes to fwk were necessary in another project (lisa_pm_adc) for its MicroBlaze software.

See fpgafw/fwk!61 (merged).

This existing software project needed a some changes to be compatible:

• set ::fwfwk::AppName in the config file instead of implicitly giving it the name of the project
• add the linker script that is initially generated by Vitis

This only affects the software that is built for the ARM Cortex-A53. When comparing the ELF files generated by this project before and after this change, all section headers are identical except some debug sections. This gives me confidence that the binaries are equivalent.