The RTD2141B has the same update protocol as RTD2142, but the Chromebook
targets that use it require us to find the drm_dp_aux_dev i2c channel
differently because the AMD display driver doesn't give each output a
unique name in sysfs, so it must be found by walking sysfs from the drm
device representing an output.
Change-Id: Icb6c1a40b8a62af72808d68a0a69555810abc272
There are now multiple plugins using drm_dp_aux_dev interface which
may potentially be combined with an amdgpu. Prevent exercising this
interface with any plugin using DP aux unless a new enough kernel is
installed.
