Use m25p128 behavioral VHDL model from Numonyx directory in $UNB.

- avoids need to compile the model in ip_stratixiv_lib, because it needs to be compiled first and should not be in the synth_files key.
- use model from Numonyx directory in $UNB, instead of the stripped copy in $UNB epcs/tb/vhdl/m25p128_model.
- Numonyx is now part of Micron company, but still keep it in the name.