Make AMBA package importing explicit

[lordspacehog]

Type of change: other enhancement

Impact: no functional change

Development Phase: implementation

Release Notes
Updates AMBA to use standalone diplomacy module directly.

Fixes a small issue with builds using chisel source for diplomacy module.

[jerryz123]

I can't comment on the mill changes, but the import package name change looks good.

Side note: we should probably run some linter to discard unused imports at some point.

[lordspacehog]

Agreed. I'm trying to fold in moving from wildcard imports to qualified imports in these changes to at least make things a little more traceable. once i get these all in, i'd love to decide on a set of scalafmt and scalafix rules to apply to the repo as well.

[sequencer]

I changed PR name to "Make AMBA package importing explicit"

[sequencer]

Side note: we should probably run some linter to discard unused imports at some point.

I propose adding scalafix

[lordspacehog]

I plan to try and push through the rest of these import updates this week, after that i'll do a separate PR adding scalafix to the build.