Add snapsafety features to VMClock device

[bchalios]

Changes

Implement snapshot safety features for VMClock device as described in this Linux patchset: https://lore.kernel.org/lkml/[email protected]/.

Expose the vm_generation_counter field in the vmclock_abi. Also, implement the notification feature. This simply means that during snapshot resume we bump vm_gneration_counter and inject an interrupt to the guest before resuming vCPUs.

Reason

Provide a means for the guest userspace to know that the microVM has been loaded from a snpahost

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 checkbuild --all to verify that the PR passes
  build checks on all supported architectures.
• 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

❌ Patch coverage is 91.04478% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.24%. Comparing base (a8f5d78) to head (91e36e2).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/vmm/src/devices/acpi/vmclock.rs	87.09%	4 Missing ⚠️
src/vmm/src/arch/aarch64/fdt.rs	91.66%	1 Missing ⚠️
src/vmm/src/device_manager/persist.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5564   +/-   ##
=======================================
  Coverage   83.24%   83.24%           
=======================================
  Files         277      277           
  Lines       29263    29309   +46     
=======================================
+ Hits        24359    24398   +39     
- Misses       4904     4911    +7     

Flag	Coverage Δ
5.10-m5n.metal	83.58% <90.90%> (+<0.01%)	⬆️
5.10-m6a.metal	82.92% <90.90%> (+0.01%)	⬆️
5.10-m6g.metal	80.26% <85.71%> (+0.06%)	⬆️
5.10-m6i.metal	83.58% <90.90%> (+<0.01%)	⬆️
5.10-m7a.metal-48xl	82.91% <90.90%> (+<0.01%)	⬆️
5.10-m7g.metal	80.26% <85.71%> (+0.06%)	⬆️
5.10-m7i.metal-24xl	83.55% <90.90%> (+<0.01%)	⬆️
5.10-m7i.metal-48xl	83.55% <90.90%> (-0.01%)	⬇️
5.10-m8g.metal-24xl	80.26% <85.71%> (+0.06%)	⬆️
5.10-m8g.metal-48xl	80.26% <85.71%> (+0.06%)	⬆️
6.1-m5n.metal	83.61% <90.90%> (+<0.01%)	⬆️
6.1-m6a.metal	82.94% <90.90%> (-0.01%)	⬇️
6.1-m6g.metal	80.26% <85.71%> (+0.06%)	⬆️
6.1-m6i.metal	83.60% <90.90%> (-0.01%)	⬇️
6.1-m7a.metal-48xl	82.93% <90.90%> (+<0.01%)	⬆️
6.1-m7g.metal	80.26% <85.71%> (+0.06%)	⬆️
6.1-m7i.metal-24xl	83.61% <90.90%> (+<0.01%)	⬆️
6.1-m7i.metal-48xl	83.62% <90.90%> (+<0.01%)	⬆️
6.1-m8g.metal-24xl	80.25% <85.71%> (+0.06%)	⬆️
6.1-m8g.metal-48xl	80.26% <85.71%> (+0.06%)	⬆️

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