drm/amdgpu: enable RAS IH for poison consumption

Enable RAS IH if poison consumption handler is implemented.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Mohammad Zafar Ziya <Mohammadzafar.ziya@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>