Revert "drm/amd/display: Don't return ddc result and read_bytes in same return value"

This reverts commit 8a61bc08.

Need to revert "make dm_dp_aux_transfer return payload bytes instead of
size", which this commit is based on. That commit was problematic on
other OSes. The real solution is to leave all the error checking to DRM
and don't do it in DC, which is addressed by "Return aux replies
directly to DRM" later in this patchset.

v2: Add reason for revert.

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