iic_acquire_bus() / iic_release_bus(). "acquire" and "release" hooks
no longer need to be provided by back-end controller drivers (only if
they need special handling, e.g. powering on the i2c controller).
This results in the removal of a bunch of rendundant code from each
back-end controller driver.
Assert that we are not in hard interrupt context in iic_acquire_bus(),
iic_exec(), and iic_release_bus().
601e178380