Add ability to poweroff ADNS5050 sensor

[ColinKinloch]

This adds the ability to poweroff the ADNS5050 sensor and set this to happen on suspend_power_down_user for the ploopy nano.

As the LED on the trackball points up it can be a little annoying when the computer is suspended/off.

I'm on the fence as to whether this should be the default for the ploopy as it would stop the trackball from being used to wake the computer.

Types of Changes

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

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).

[fauxpark]

Is it necessary to reinit on wake?

[ColinKinloch]

I think so:
From page 16 of https://media.digikey.com/pdf/Data%20Sheets/Avago%20PDFs/ADNS-5050.pdf

There are 2 ways to exit power down, either assert low NRESET pin or by writing 0x5a to Register 0x3a. A full reset will thus be executed.

[drashna]

You missed the most important part of that paragraph:

Any register settings must then be reloaded.

So yeah, it sounds like a re-init would be appropriate in this case.

I would say pull out the register init into a separate function, but this sensor doesn't run i2c/spi/uart init, so should be fine, as is, I think.