add wit dependency/git submodule check to travis

Fix TraceGen issues and allow it to use NonBlockingDCache

Add filename option

tilelink: correct fragmenter helper

Debug: interface and attachment parameterization

- adds an enum describing the exported protocol type
- adds a param case class consolidating the various interface options
- adds a config field to supply instance of said params to design

TileLink: UserUniformer

The CSR address from the wrong pipeline stage was used when detecting
whether the DRET instruction was valid, causing spurious exceptions.

dret should be illegal outside debug mode

tilelink: add UserUniformer to fill in default UserBits values for clients that dont provide user bits of the specified type