drm/amd/powerplay: disable Vega20 DS related features

Disable these features on Vega20 for now.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Feifei <Xu&lt;Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>