This commit:
- Finds a common set of board feature tags and maps existing features to
  that reduced set.
- Removes some less-useful board feature tags.
- Ensures all MCUs are specified correctly.
- Ensures all boards have a vendor (and fixes some vendor names).

This is to make the downloads page show a less intimidating set of filters.

Work done in conjunction with Matt Trentini <matt.trentini@gmail.com>.

This work was funded through GitHub Sponsors.
Signed-off-by: NJim Mussared <jim.mussared@gmail.com>