Add support for `KVM_CAP_X86_SMM` / `KVM_SMI`

[00xc]

Summary of the PR

Allow VMMs to inject System Management Interrupts (SMIs) into the guest via the KVM_SMI vcpu ioctl, which is available if the KVM_CAP_X86_SMM capability is present.

Requirements

• [X] All commits in this PR are signed (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [X] All added/changed functionality has a corresponding unit/integration test.
• [X] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [X] Any newly added unsafe code is properly documented.

[00xc]

Reordered Cap::X86Smm to keep a consistent ordering.

[00xc]

Rebased on main, fixed conflicts and fixed a formatting error in the changelog.