RMII

[owenthewizard]

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Submission Checklist 📝

• I have updated existing examples or added new ones (if applicable).
• I have used cargo xtask fmt-packages command to ensure that all changed code is formatted correctly.
• My changes were added to the CHANGELOG.md in the proper section.
• I have added necessary changes to user code to the latest Migration Guide.
• My changes are in accordance to the esp-rs developer guidelines

Extra:

• I have read the CONTRIBUTING.md guide and followed its instructions.

Pull Request Details 📖

Description

Implement RMII bus. Motivation: Ethernet support (LAN87xx, IP101GRI, ...).

Testing

Describe how you tested your changes.