[WIP] mirny: add

[jordens]

• This targets the CPLD gateware at https://github.com/quartiq/mirny
• includes initial coredevice driver, eem shims, and kasli_generic tooling
• addresses the ARTIQ side of Mirny support #1130
• Register abstraction to be written

Test report from @airwoodix:

• on a fresh power-up, it needs two tries to lock (artiq_run twice);
• the MUXOUT=DVDD check in ADF5355.init fails randomly when
  manipulating reg1. It might be a delay thing, haven't investigated
  systematically yet;
• the clk_sel documentation in the gateware code seems wrong to
  me. The schematics has in_sel0 and in_sel1 exchanged. The easiest
  might be to exchange the pins in the platform description.

ARTIQ Pull Request

Description of Changes

Related Issue

Closes #1130

Type of Changes

	Type
	🐛 Bug fix
✓	✨ New feature
	🔨 Refactoring
✓	📜 Docs

Steps (Choose relevant, delete irrelevant before submitting)

All Pull Requests

• Use correct spelling and grammar.
• Update RELEASE_NOTES.md if there are noteworthy changes, especially if there are changes to existing APIs.
• Close/update issues.
• Check the copyright situation of your changes and sign off your patches (git commit --signoff, see copyright).

Code Changes

• Run flake8 to check code style (follow PEP-8 style). flake8 has issues with parsing Migen/gateware code, ignore as necessary.
• Test your changes or have someone test them. Mention what was tested and how.
• Add and check docstrings and comments
• Check, test, and update the unittests in /artiq/test/ or gateware simulations in /artiq/gateware/test

Documentation Changes

• Check, test, and update the documentation in doc/. Build documentation (cd doc/manual/; make html) to ensure no errors.

Git Logistics

• Split your contribution into logically separate changes (git rebase --interactive). Merge/squash/fixup commits that just fix or amend previous commits. Remove unintended changes & cleanup. See tutorial.
• Write short & meaningful commit messages. Review each commit for messages (git show). Format:

  topic: description. < 50 characters total.
  
  Longer description. < 70 characters per line
  

Licensing

See copyright & licensing for more info.
ARTIQ files that do not contain a license header are copyrighted by M-Labs Limited and are licensed under LGPLv3+.