drm/amdgpu: Fix aldebaran MMHUB CG/LS logic

Aldebaran MMHUB CG/LS logic is controlled by VBIOS. Enable the state
change logic only if driver is used for control.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>