alsa-mixer: Add an profile for EVO4 interface

The Audient EVO4 USB audio interface supports loopback audio, so the desktop audio set out to it can also be included back into the input audio. In some situations this is not what you want (e.g. when you use it for conference calling).

This change introduces and additional profile which disables loopback audio so the user can choose whether loopback audio is enabled or not.

I've also blogged about the issue here: https://writepermission.com/evo4-pulseaudio-profile.html