Revert "drm/amdgpu/disply: fix documentation warnings in display manager"

This reverts commit 6ae09fa4.

Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Alexander Deucher <Alexander.Deucher@amd.com>
Cc: Harry Wentland <Harry.Wentland@amd.com>
Cc: Roman Li <Roman.Li@amd.com>
Cc: Bindu R <Bindu.R@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>