drm/amdgpu: use direct loading on renoir vcn for the moment

PSP has issue for renoir, that will cause VCN fw failed to be loaded. So use
direct loading for the moment till the issue is addressed.

Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Aaron Liu <aaron.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>