targets: Rename rp2040 directory to rp2 Change-Id: I73f56cc3330351b087ed331bec483271dd37828c Reviewed-on: https://pigweed-internal-review.git.corp.google.com/c/pigweed/showcase/rp2/+/72151 Commit-Queue: Armando Montanez <amontanez@google.com> Reviewed-by: Taylor Cramer <cramertj@google.com> Presubmit-Verified: CQ Bot Account <pigweed-internal-scoped@luci-project-accounts.iam.gserviceaccount.com>