drm/amd/display: Add copyright notice to new files

Reviewed-by: Shahin Khayyer <Shahin.Khayyer@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>