FPGA Makefile refactoring

Created by: jordancarlin

@ross144 If you're interested, this new version of the makefile allows you to run make for the different FPGA boards without having to comment out a variety of different lines. You can either just change the all target to point at the board you want or run make [ArtyA7|vcu108|vcu118] directly from the command line to compile for a specific board. I've kept the default board as the ArtyA7.