amdgpu/pm: Disallow managing power profiles on SRIOV for Sienna Cichlid

Managing power profiles mode is not allowed in SRIOV mode for Sienna
Cichlid. This patch is adjusting the "pp_power_profile_mode" and
"power_dpm_force_performance_level" accordingly.

Signed-off-by: Danijel Slivka <danijel.slivka@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>