switch-on-port-available: Switch to headphones on unknown availability

Since not all users will have environments that asks what they plugged in when their hardware supports TRRS inputs but don't have impedance sensing, let's emulate our previous default behaviour of enabling the headphone port at least.

This can likely be improved so users can configure the module to select for the device they are most likely to plug in (so an option to enable just the microphone, or headphones+headset-mic ports).

Fixes: #1028 (closed)