Add I2C device hints for Onion Omega

This allows you to control up to 8 relay expansions from FreeBSD

https://github.com/freebsd/freebsd-wifi-build/wiki/Onion-Omega#controlling-the-relay-expansion

Reviewed by: adrian, mizhka
MFC after: 1 week
Sponsored by: ScaleEngine Inc.
Differential Revision: https://reviews.freebsd.org/D9503