i2c(PCA9685, adafruit): clean up architecture and fix init

[gen2thomas]

Solved issues and/or description of the change

• adafruit_driver.go contains shared variables and init() #1010
• PCA9685 wrong initialisation #1020
• write /dev/i2c-1: remote I/O error on Raspberry Pi Zero 2 W and Adafruit Motorhat #809

Manual test

• OS and Version (Win/Mac/Linux): Linux
• Adaptor(s) and/or driver(s): Tinkerboard & adeept motor HAT 2.0

Checklist

• The PR's target branch is 'hybridgroup:dev'
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes (e.g. by run make test)
• No linter errors exist locally (e.g. by run make fmt_check)
• I have performed a self-review of my own code

If this is a new driver or adaptor:

• I have added the name to the corresponding README.md
• I have added an example to see how to setup and use it
• I have checked or build at least my new example (e.g. by run make examples_check)