MCY example for verilator testbench

Created by: nakengelhardt

An example project that demonstrates how to use mcy.

This was mostly written to stay self-contained in the cv32/sim/mcy directory and not touch existing files, which leads to a lot of duplication. Needs discussion how to integrate.

The main issue is the makefile/build instructions. The makefile from core uses relative paths for includes so can't be launched in any other folders, but if the build instructions are duplicated they will diverge. The manifest for building the mutated design could perhaps be derived from the original with a sed script, so that it would automatically work with new code for small changes.

The reduced firmware that only runs the tests for the division instructions also contains a lot of duplicated files. It could be integrated as ifdefs, or moved inside the mcy folder so it doesn't clutter up the regular test files.