FR: Encryption: Add option to use xchacha12 (instead of xchacha20)

[JustMyGithub]

It is great that sdm offers xchacha20, but is there a reason why users cannot choose xchcha12? That would provide even a little more performance on pi4, right?

[gitbls]

Looks like xchacha12 provides about 25% faster decryption, which is fairly good. Adding this to the TODO list.

Thanks for the suggestion!