drm/amdgpu/discovery: Add sw DM function for 3.1.6 DCE

Add 3.1.6 DCE IP and assign relevant sw DM function for the new DCE.

Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>