Get Lakeroad+Yosys integration merged into Yosys

[gussmith23]

Tasks:

• Move all of the Lakeroad-related stuff onto its own branch
• Make Lakeroad stuff build optionally; connect it to an external Lakeroad with the Yosys plugin system
• Clean up Lakeroad and document it so that it can be externally used
• Open PR on Yosys

[gussmith23]

This seems to be the mention of GHDL in Yosys source:
https://github.com/YosysHQ/yosys/blob/320e75a3e3322419a70a8cf9e7f774880c5800fc/Makefile#L518-L524

[gussmith23]

Nina pointed me the actual plugin demo:
https://github.com/YosysHQ-GmbH/tabby-cad-plugin-build
See the hello world example: it actually loads a .so into prebuilt Yosys. Very nice! So you can use a prebuilt Yosys.