Canonicalize SMP topology and shared interrupt status

Tracking issue: MicroVM support and private snapshot restore.

Motivation

An SMP microVM needs one consistent description of its processors across machine
configuration, guest tables, interrupt routing, and saved state. Canonical topology
and shared interrupt-status semantics make multi-processor boot and restore
reviewable and avoid backend-dependent interpretations of the same machine.

Proposed Scope

• Define a canonical topology and stable VP identities for supported microVM SMP
  configurations.
• Apply the topology consistently to guest discovery, processor construction, and
  snapshot compatibility checks.
• Define shared-status interrupt delivery, including how pending sources are
  observed and cleared without losing another source's notification.
• Introduce required ACPI fields and update every affected platform constructor
  and caller in the same PR.
• Preserve the single-VP profile and previously established restore behavior.

Acceptance Criteria

• Equivalent valid configurations produce the same topology and VP identities
  across supported boot and restore paths.
• Invalid processor counts, identifiers, or incompatible restored topology
  fail before guest execution.
• Deterministic tests cover multiple pending interrupt sources and clearing one
  source while another remains pending.
• VMM coverage boots and restores a supported multi-VP guest and verifies
  processor discovery, execution, and interrupt delivery.
• Windows and Linux callers compile with all required ACPI initialization;
  no later PR is needed to complete the API change.
• The canonical topology and supported limits are documented.

Dependencies

• D03: Filesystem persistence and attachment revalidation
  precedes this integration step so SMP validation covers the complete device set.

This ordering is an integration prerequisite, not a claim that CPU topology
inherently depends on a filesystem device.

Non-Goals

This issue does not introduce arbitrary CPU hotplug, cross-topology migration, or
the later policy for selecting VP targets during restore.

Start with the linked 00-microvm.md tracking document and review dependency issue #4441 before mapping the affected platform constructors and callers. Use the acceptance criteria as the completion checklist: canonical topology and VP identities, validation before guest execution, interrupt-source tests, multi-VP boot and restore coverage, complete ACPI initialization, and documentation of limits.