drm/amdgpu/sriov: Tonga sriov also need load firmware with smu

Fix Tonga sriov load driver fail issue.

Signed-off-by: Emily Deng <Emily.Deng@amd.com>
Reviewd-by Yintian Tao <Yintian.tao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>