drm/amdgpu: enable xgmi support for Aldebaran

Like its predecessors Aldebran also supports advanced high bandwidth
GPU-GPU communication interface known as xgmi. This enables the basic
xgmi support while refactoring the code slightly.

Detection of xgmi link between host cpu and gpu will be introduced in a
different patch.

Reviewed-by: Oak Zeng <oak.zeng@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>