Add support for gf180mcu

[mithro]

Currently it doesn't look like bazel_rules_hdl supports GF180MCU PDK? It would be good to support that PDK.

[mithro]

I thought I had added support for GF180MCU at some point but maybe that was only internally in Google3? @QuantamHD - Could you take a look and see if there is something that could/should be exported to this repo?

[QuantamHD]

Sure. I'll take a look Monday. I don't recall it being in google3