[machine_pkg] Changes in Vivado version breaks blk_mem_gen for Modelsim

[aylons]

As Vivado's version changes, the version Modelsim has compiled may differ from the version generated, creating conflicts that do not have any meaning on RTL simulations.

Xilinx's blk_mem_gen ip core, as used in this project, is a very simple core to simulate on a RTL level - it is only a look-up table. A solution may be to generate a modelsim-friendly version for each machine_pkg that is selected by hdlmake while generating a simulation Makefile.