aw20216: driver naming cleanups

[fauxpark]

Description

Renamed driver to AW20216S per below comment, and added AW20216S_ prefix to all defines.

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).

[sigprof]

BTW, this driver is actually for the AW20216S chip (full part number is AW20216SQNR): https://www.awinic.com/en/productDetail/AW20216SQNR. The current driver name is confusing, because the AW20216 (AW20216QNR) chip also exists: https://www.awinic.com/en/productDetail/AW20216QNR, but that chip uses I2C, not SPI.

Looks like the register layout for AW20216 and AW20216S is actually the same, and the only differences are related to the I2C or SPI access (the SPI variant uses a 2-byte prefix before data that specifies both the page and register address; the I2C variant uses a separate register for switching pages, similar to what various ISSI chips do). But with the current QMK infrastructure those chips would require separate drivers anyway.