Support SKY130

[donn]

Self-explanatory. We don't need to mess around with OSU or Nangate now that we have an honest to goodness open source PDK.

That, and Fault is supposed to be integrated into OpenLane someday. So.

[widlarizer]

Why not support all flip flops supported by Yosys?

[donn]

We'd need to source a competent lib file parser and somehow extract which cells are flip-flops: cut doesn't use Yosys for example, but it is essential for ATPG. I recall Yosys having a similar cutaway function but I removed it in e20d40b because it was fairly buggy.

Just using a reg is a neat idea though- we ARE already using Yosys techmap after chaining so why not dfflibmap.