alsa-ucm: Simplifications assuming we have one device per mapping
requested to merge alpernebbi/pulseaudio:alsa-ucm-one-mapping-per-device-simplifications into master
These are some code simplifications on top of !664 (closed) based on the result that we will no longer generate combination ports after it, since that MR makes the mapping names based on the UCM verb+device name which is unique per UCM device.