Add defmt feature and derive error types

[jbeaurivage]

Summary

Add defmt feature, and derive defmt::Format for the HAL's error types.

Closes #522.

Checklist

• CHANGELOG.md for the BSP or HAL updated
• All new or modified code is well documented, especially public items
• No new warnings or clippy suggestions have been introduced (see CI or check locally)

If Adding a new cargo feature to the HAL

• Feature is added to the test matrix for applicable boards / PACs in crates.json