Added PMW3320 driver

[Vladeeg]

Description

Added support for Pixart PMW3320 optical sensor.

Since PMW3320 sensor's datasheets are not really descriptive in terms of programming and I don't really have experience in hardware reverse engineering, some parts of implementation are guesses.

I used ADNS5050 driver as a base for this driver, so some "hacks" are from here.

I'm pretty sure that some initial settings in pmw3320_init function are device-specific, but haven't found any similar settings for other sensor in other devices folders, so I'm not sure where to put them.

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

None

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). Specifically, I tested it on my own Elecom Huge trackball, and I have a branch for it in my fork repo: https://github.com/Vladeeg/qmk_firmware/tree/feature/elecom-huge-atmega

[drashna]

Aside from the register comment, it looks good

[drashna]

For now, the driver appears to be fine, as is.

Most of my feedback is "it might be better", but isn't strictly required.