drm/amdgpu: Disable DPM in virtualization

This patch is used for virtualization support. In virtualization,
only SMU manager is needed, DPM should be disabled. This is a
use case for commit 2f9346b6f984
("drm/amdgpu/powerplay: pp module only enable smu when dpm disabled.")

Signed-off-by: Trigger Huang <trigger.huang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>