Only really required for dp 1.2. I've hoped this would help with some
link training woes I'm fighting, but alas those are only dp 1.1
devices.

Also move a comment that went misplaced in the recent refactorings to
the right spot again.
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>