[usbdev_swdrive_test] SW pin driving test

[alees24]

Passing Verilator top-level test that exercises software pin driving, using a new bypass mode in the interface to the DPI model. Software-driven outputs are propagated straight back to the input pins independently, to permit full checking of pins_drive/sense functionality. Annotated usbdpi.sv logic because there are many signals with very similar names.

[rswarbrick]

Hi @alees24! I'm working through old usbdev PRs and this was the oldest(!). I've just rebased it to the current head of master. Is this still something you're working on?

[alees24]

Hi @alees24! I'm working through old usbdev PRs and this was the oldest(!). I've just rebased it to the current head of master. Is this still something you're working on?

It got lost in the review process a long time ago. It still has relevance, since it's still the only test that exercises the sw drive and sense registers/functionality, and it's something that can only be done in Verilator chip-level simulation (as performed here) or block level DV (not yet done).

I have updated the BUILD file to accommodate subsequent changes and re-tested with Verilator,