Fix "fusesoc tool list" with edalize 0.6.2+

[jmerdich]

Edalize removed the methods previously used to list the tools (walk_tool_packages). Use the new methods when present.

[jmerdich]

Fixes #755

[olofk]

Thanks for this. Functionality looks fine, but the code doesn't pass the formatting check. Make sure you run black on the code to format this properly. Easiest way is to set it up as a pre-commit hook by running pre-commit install in your local repo. This will do a formatting check every time you commit.