drm/amdgpu: Implement get num of hops between two xgmi device

KFD need to provide the info for upper level to determine the data path

Signed-off-by: shaoyunl <shaoyun.liu@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>