keep/update config.sh file #502

• Except for two actual values, all the rest is made of no-op AAAA=${AAAA:-} statements. That's very misleading from a coding perspective.
• What would be more useful is a local config file that is not in git so it doesn't pollute git diff and git status (and even git add * - never do that)
• I'm not even sure a single file collecting all default values is a good idea. Most software seems to have good defaults even when run with empty config files.

Quoting @marc-hb from #498 (comment)

With above issues for config.sh file, we need some new design with configuration for sof-test for customize usage.

area:non-audio Failure False positives: failing when we don't want to