drm/amd/powerplay: fix deadlock on setting power_dpm_force_performance_level

smu_enable_umd_pstate() will try to get the smu->mutex which was already
hold by its parent API smu_force_performance_level() on the call path.
Thus deadlock happens.

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