drm/amdgpu: remove duplicate cg/pg wrapper functions

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian <König&lt;christian.koenig@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>