feat(boards): Add waveshare rp2040 board definition

[Nick-Munnich]

This PR builds off of #2596, fixing the problems Pete noted there alongside some other changes. As of two weeks ago, Zephyr's main branch has this board as well, so the name was adjusted to match with it.

Figured since I needed to update the PR for my own stuff anyway I may as well PR the updated version.

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.