of: unitest: Add I2C overlay unit tests.

Introduce I2C device tree overlay tests.
Tests insertion and removal of i2c adapters, i2c devices, and muxes.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Signed-off-by: Rob Herring <robh@kernel.org>
(cherry picked from commit d5e75500ca401d3128c82c5b0dee2f9b259d5b5c)
Signed-off-by: Mark Brown <broonie@kernel.org>
3 files changed