drm/amd/display: Return aux replies directly to DRM

Currently we still go through DC code that does error checking, retries,
etc. There's no need for that since DRM already does that for us. This
simplifies the code a bit and makes it easier to debug.

This also ensures we correctly tell DRM how many bytes have actually
been read, as we should. This allows DRM to correctly read the EDID on
the Chamelium DP port.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>