Add waveform with iverilog simulator

[mamin506]

This PR is to support Waveform output for Icarus Verilog simulator.

How to generate waveform,

# A new target test.test_% is added. Based on the design of this project, % is matadd or matmul.
# To generate waveform for matadd test, run
$ make test.test_matadd

# The generated waveform file is sim_build/gpu.fst. Use gtkwave to open.