zero: introduce adaptor for Radxa Zero

[gen2thomas]

Solved issues and/or description of the change

#1114

Manual test

• OS and Version (Win/Mac/Linux): Linux
• Adaptor(s) and/or driver(s):
  • GPIO
  • PWM
  • I2C
  • ADC
  • 1-wire
  • SPI (not working yet, because bug in DT-overlay)

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_race)
• 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)