[Core] STM32G0x1 support

[KarlK90]

Description

This adds support for the stm32g0x1 line of mcus which is the spiritual successor of the stm32f072 line.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[tzarc]

Bootloader might need some messing about with. By default the option bytes disable BOOT0 on a physical pin, IIRC. That, along with dual-bank flash make things a bit difficult to reflash once a firmware is present.