Early init drm_dp_aux for internal use before i2c-core is ready

In order to break a chicken-and-egg problem in wanting to use i2c_transfer on the drm_dp_aux before it is registered with userspace (which is a requirement for i2c_add_adapter() sadly), we need to prepare enough state internally so that drm_dp_aux->algo->master_xfer() is operation. A trio of patches to expose this operation from i2c has been sent, which we can plug in here to replace the open-coding. I want to get the ball rolling on this as I have a regression fix pending getting i915 init reordered. -Chris