Merges support for functional coverage into wally.do and testbench.sv

Created by: rosethompson

This is bit hacky and will need to be cleaned up with future commits. However, I have the base features finally working. ImperasDV and riscvISACOV both work with wally.do, wsim, and testbench.sv and don't require any outside scripts.

To run functional coverage add the flag --fcov to wsim and run with a single elf file.

I've confirmed coverage is generated in the GUI.