drm/amdgpu: force enable gfx ras for vega20 ws

Signed-off-by: Stanley.Yang <Stanley.Yang@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>