drm/amdgpu: remove perf level dpm in one-VF

On Navi12 platform, node power_dpm_force_performance_level
doesn't work correctly in one-VF mode with at least three
smu messages not supported:
SMU_MSG_SetSoftMaxByFreq
SMU_MSG_SetSoftMinByFreq
SMU_MSG_TransferTableDram2Smu

Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Signed-off-by: Wenhui Sheng <Wenhui.Sheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>