Build Yosys integration: annotations on modules to map to one or more DSPs

[gussmith23]

Talking to the Yosys people, I think we've landed on a Yosys+Lakeroad integration that actually sounds interesting to them and feasible to us. The idea was this: give designers the ability to annotate modules, saying e.g. "this module should go onto N DSPs", and then have a Yosys pass that actually compiles it onto that many DSPs (via Lakeroad).

[gussmith23]

Development in uwsampl/yosys#3