drm/amdgpu: do not disable SMU on vm reboot

For passthrough device,  we do baco reset after 1st vm boot so
if we disable SMU on 1st VM shutdown baco reset will fail for
2nd vm boot.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>