Move RGBLight code into its own folder

[fauxpark]

Description

More tidying up of quantum/.

@MxBlu The changes to the mxss rules.mk results in a different MD5, but the firmware size is exactly the same, and it appears the only difference is in the order of compilation (and thus linkage) of a couple of files so I don't think I've broken anything.

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).

[MxBlu]

Likely fine, I'll test it out (and apologies again for the maintainance task, I'll put an effort into getting rid of the localised ver of rgblight.c in the coming months hopefully)