drm/amd/pm: revise the performance level setting APIs

Avoid cross callings which make lock protection enforcement
on amdgpu_dpm_force_performance_level() impossible.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>