drm/amdkfd: expose host gpu link via sysfs (v2)

Currently host-gpu io link is always reported as PCIe however, on some
A+A systems, there could be one xgmi link available. This change exposes
xgmi link via sysfs when it is present.

v2: fix includes (Alex)

Reviewed-by: Oak Zeng <oak.zeng@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>