drm/amd/powerplay: drop unnecessary wrappers

These APIs are used in amdgpu_smu.c only. Thus these wrappers
are unnecessary.

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