drm/amdgpu: Power down VCN and JPEG before disabling SMU features

When unloading driver, if VCN is powered on, sending message
DisableAllSmuFeatures to SMU will cause SMU hang. We need to
power down VCN and JPEG before clean up SMU.

Signed-off-by: Chengzhe Liu <ChengZhe.Liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>