drm/amdgpu: support get xgmi information for Aldebaran

Aldebaran uses registers defined in header gc_9_4_2 but much of the xgmi
related functionality can be obtained by reusing the exisitng definition
from gfxhub_v1_1_get_xgmi_info. While adding support for Aldebaran, also
refactored code to better handle the new scenario.

Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>