fastrpc: validate DT-declared domain registration

[Srikanth Muppandam (smuppand)]

Summary

Address the registration-failure concern raised for commit 789a821: a healthy discovered DSP must not hide another enabled FastRPC DT domain that failed to register.

• Derive expectations from enabled runtime FastRPC DT nodes, labels and ancestor status, without board/SoC lists.
• Include expected domains in automatic selection. Missing/offline registration, endpoints or required runtime libraries record FAIL while healthy domains continue.
• Check expected kernel registration before missing-binary SKIP or existing package-provider handling.
• Preserve failures across later shared-asset/no-runnable-domain SKIPs.
• Retain DT evidence and add operator documentation and host regression fixtures.

Policy and compatibility

Automatic mode uses current enabled DT declarations and runtime capabilities only. CDSP absent from both creates no historical requirement. Other domains continue, or none applicable produces SKIP. Removed/disabled DT intent belongs to triage. Runtime-discovered domains remain eligible without a DT declaration. Explicit --domain-name selection retains its scope and fails when unavailable.

No board lists, mandatory-domain CI option, YAML changes or new package-installation paths. Existing healthcheck preference, remoteproc fallback and distro package policy are retained. Preflight does not load modules, start remoteprocs or create endpoints.

Validation

• PASS: 4 absence-policy checks with real DT parsing and runner selection/finalization using mocked hardware.
• PASS: 16 full-runner startup checks under Cygwin dash, including registration failures before missing-binary handling, explicit selection, discovery errors, ADSP-only operation and provider outcomes.
• PASS: ShellCheck 0.9.0, dash syntax, YAML parsing, result-name/publication checks and git diff --check.
• Verified executable runner mode and DCO sign-off.

Pending validation

• Execute the full fastrpc-domain-validation.sh matrix on native Linux. Earlier broad-matrix attempts did not complete on this Windows host.
• Obtain FastRPC DUT/LAVA evidence with and without healthcheck across Yocto, Debian, Ubuntu and CentOS paths.

Host fixtures perform no DSP operations or package installation and do not prove hardware/cross-distro behavior. Pending validation is tracked in the local TODO queue. This PR is intentionally a draft.