audio: add generic remoteproc-aware Shikra playback and record validation

[Srikanth Muppandam (smuppand)]

Fixes #543

Summary

• Add generic audio remoteproc preflight for playback and record validation.
• Dynamically enumerate remoteprocs through shared functestlib.sh helpers.
• Prioritize a modem-hosted audio path by runtime remoteproc name without assuming a remoteproc index.
• Validate image-provided firmware and topology before starting an offline audio remoteproc.
• Fail when an offline modem audio remoteproc is missing its required topology.
• Preserve already running remoteprocs and never stop them.
• Reject PipeWire camera and dummy nodes as physical microphone or speaker devices.
• In auto mode, fall back to capability-discovered ALSA routes when no physical managed audio device exists.
• Preserve explicit PipeWire, PulseAudio, and ALSA backend requests.
• Apply mixer controls only when present on the discovered ALSA card.
• Document backend selection, ALSA routing, remoteproc behavior, and ALSA support in suite READMEs and YAML metadata.