drm/amdgpu: Use switch case for unique_id

To ease readability, use switch to set unique_id as supported for the
supported IP_VERSIONs, and set it to unsupported by default for all
other ASICs.
This makes it easier to add IP_VERSIONs later on, and makes it obvious
that it is not supported by default, instead of the current logic that
assumes that it is supported unless it is not one of the specified
IP_VERSIONs.

v2: Rebase onto previous IP_VERSION change

Signed-off-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Kevin Wang <KevinYang.Wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>