drm/amd/powerplay:Tonga not to start SMC if SRIOV

This patch is used for virtualization support. In virtualization case,
Tonga SMC should not be started and SMU firmware should not be loaded
if in SRIOV environment. The same operation will be applied on FIJI in
other patch.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Signed-off-by: Trigger Huang <trigger.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>