LED drivers: add support for shutdown pin

[fauxpark]

Description

Long overdue...

This adds support for specifying a pin to set as output high connected to the SDB pin of the LED driver(s), which should eliminate a small bit of code at the keyboard level for those boards which do not simply have it tied to VCC.

Note that only one pin is supported, as if you have multiple drivers on a board it seems unlikely you would want to control them independently. The AW20216S driver does this but as far as I can tell every board currently in the repo which uses it uses the same pin for both defines, so I will probably rework that in future.

This is also a very basic implementation to start with - all it does is set the pin high during init_drivers(); there is currently no logic to toggle the SDB signal when the board suspends/wakes, but this could be added later.

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).