Bring back support for volume control endpoints

[SebuZet]

I've restored support for Volume Control Endpoints.
I'm using this functionality to control volume on my Soekris R2R DAC (dam1021) using built-in HW volume control.
As an example of usage you can see my dac extension:

https://github.com/SebuZet/soekris_dac_roon

[pavoni]

Thanks @SebuZet - I'll take a proper look at this.

Could you add an example of how to use this code to the examples directory?

It's in lieu of documentation for anyone looking to use it (including me!)

[pavoni]

Thanks for this.

My main request is for you to add an example of using this part of the api to the examples directory (mainly because it acts as simple documentation)

There also looks to be a formatting issue that to automatic build process caught.

[pavoni]

This assignment is duplicated

[pavoni]

Just wanted to check if you're still planning to complete this? Otherwise will close the PR.

[pavoni]

Closed since it's gone stale. Happy to re-open...