drm/amd/powerplay: add new smu ip block

This patch add amdgpu_smu ip block skeleton as placeholder.
We plan use new smu ip block from Vega20.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>