superio+nctgpio: Prepare to support some new (weird) chips
- Increase verbosity to direct i/o code path (iores != 0)
- Fix pin inversion configuration
- Allow forcing the use of indirect access channel via hint.gpio.0.flags=2
- Document the PREFER_INDIRECT_CHANNEL tunable in nctgpio(4)
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/719