completion: Add value completion for more arguments

[hyperupcall]

This improves completion by:

• Properly completing directory names and path names for more flags. Basic completion for -a was also implemented (defaulting to current architecture)
• Restructure -@\(c|-spec|-archive|-config\) to something that works and is simpler. Now, even extglob does not need to be enabled for the new completion to work

[evelikov]

Amazing, thank you.

If you feel like adding zsh completion that would be very welcome. You can use the existing /usr/share/zsh/functions/Completion/Linux/_dkms as a base. Sending a message (email) to the zsh devs with a link to the PR would be perfect.

Thanks o/

[hyperupcall]

Sounds good, I will get to it if I can