refactor: move arch specific Kvm code into modules

[bchalios]

Changes

Follow up of the refactoring we did in the past around vstate/vm.rs, where we separate architecture specific code in modules, keeping only the arch-independent code in 'kvm.rs`

Moreover, move arch-specific code from vmm::vstate module under vmm::arch.

Reason

More readable code. No functional changes intended.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkstyle to verify that the PR passes the
  automated style checks.
• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
• If a specific issue led to this PR, this PR closes the issue.
• When making API changes, I have followed the
  Runbook for Firecracker API changes.
• I have tested all new and changed functionalities in unit tests and/or
  integration tests.
• I have linked an issue to every new TODO.

---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

Attention: Patch coverage is 86.36364% with 30 lines in your changes missing coverage. Please review.

Project coverage is 83.13%. Comparing base (83a9a55) to head (97f9b29).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/vmm/src/arch/aarch64/vcpu.rs	83.23%	29 Missing ⚠️
src/vmm/src/arch/x86_64/kvm.rs	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5098      +/-   ##
==========================================
- Coverage   83.14%   83.13%   -0.02%     
==========================================
  Files         248      249       +1     
  Lines       26925    26937      +12     
==========================================
+ Hits        22388    22393       +5     
- Misses       4537     4544       +7     

Flag	Coverage Δ
5.10-c5n.metal	83.51% <96.15%> (-0.03%)	⬇️
5.10-m5n.metal	83.51% <96.15%> (-0.01%)	⬇️
5.10-m6a.metal	82.70% <96.15%> (-0.02%)	⬇️
5.10-m6g.metal	79.56% <85.20%> (-0.01%)	⬇️
5.10-m6i.metal	83.50% <96.15%> (-0.02%)	⬇️
5.10-m7a.metal-48xl	82.70% <96.15%> (-0.01%)	⬇️
5.10-m7g.metal	79.56% <85.20%> (-0.01%)	⬇️
6.1-c5n.metal	83.56% <96.15%> (-0.03%)	⬇️
6.1-m5n.metal	83.56% <96.15%> (-0.01%)	⬇️
6.1-m6a.metal	82.75% <96.15%> (-0.01%)	⬇️
6.1-m6g.metal	79.56% <85.20%> (-0.01%)	⬇️
6.1-m6i.metal	83.56% <96.15%> (-0.01%)	⬇️
6.1-m7a.metal-48xl	82.75% <96.15%> (-0.01%)	⬇️
6.1-m7g.metal	79.56% <85.20%> (-0.01%)	⬇️

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[roypat]

would love to pick these commits up for the feature/secret-hiding branch!

[bchalios]

would love to pick these commits up for the feature/secret-hiding branch!

I was planning to add more changes that include builder.rs as well. But, there's a lot of overlap with #4910 and, secondly, there's a lot more complexity there, so I'm happy to format these as a standalone PR.

In the long term, I was envisioning all of the arch specific code to go under vmm::arch. WDYT @roypat?

[roypat]

would love to pick these commits up for the feature/secret-hiding branch!

I was planning to add more changes that include builder.rs as well. But, there's a lot of overlap with #4910 and, secondly, there's a lot more complexity there, so I'm happy to format these as a standalone PR.

I think this on its own makes a lot of sense as a standalone PR :)

In the long term, I was envisioning all of the arch specific code to go under vmm::arch. WDYT @roypat?

Yeah, having them be centralized would be neat indeed