drm/amdgpu: Set proper function to set xgmi pstate

Driver need to call SMU to set xgmi pstate

Signed-off-by: shaoyunl <shaoyun.liu@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>