Add a raw API for DPI intrinsics

[uenoku]

Not ready for review yet but this PR adds a raw API for DPI intrinsics and demonstrates usage. The test passes locally but requires a new version of firtool.

Contributor Checklist

• [x] Did you add Scaladoc to every public function/method?
• [x] Did you add at least one test demonstrating the PR?
• [x] Did you delete any extraneous printlns/debugging code?
• [x] Did you specify the type of improvement?
• [ ] Did you add appropriate documentation in docs/src?
• [x] Did you request a desired merge strategy?
• [ x Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Feature (or new API)

Desired Merge Strategy

• Squash: The PR will be squashed and merged (choose this if you have no preference).

Release Notes

Reviewer Checklist (only modified by reviewer)

• [ ] Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• [ ] Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
• [ ] Did you review?
• [ ] Did you check whether all relevant Contributor checkboxes have been checked?
• [ ] Did you do one of the following when ready to merge:
  • [ ] Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • [ ] Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.