drm/amdgpu: Keep non-psp path for partition switch

When PSP block is not present, use direct programming.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Mangesh Gadre <Mangesh.Gadre@amd.com>
Tested-by: Mangesh Gadre <Mangesh.Gadre@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>