drm/amdgpu: add DCI HWIP

So we can track grab the appropriate DCE info out of the
IP discovery table.  This is a separare IP from DCN.

Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>