witherspoon: Add nvlink2 interconnect information
witherspoon: Add nvlink2 interconnect information

GPUs on Redbud and Sequoia platforms are interconnected in groups of
2 or 3 GPUs. The problem with that is if the user decides to pass a single
GPU from a group to the userspace, we need to ensure that links between
GPUs do not get enabled.

A V100 GPU provides a way to disable selected links. In order to only
disable links to peer GPUs, we need a topology map.

This adds an "ibm,nvlink-peers" property to a GPU DT node with phandles
of peer GPUs and NVLink2 bridges. The index in the property is a GPU link
number.

Signed-off-by: Alexey Kardashevskiy <ac1fc56530d7d037e1ea666f130daca22d72f964@ozlabs.ru>
Acked-by: Reza Arbab <4c896a97e6b998365c2d50a267b0f1ca5f7995de@linux.ibm.com>
[stewart: fixed strtol found in review by Reza]
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.ibm.com>

shenki/skiboot,stewart-ibm/skiboot,qemu/skiboot,shenki/skiboot,shenki/skiboot,open-power/skiboot,open-power/skiboot,stewart-ibm/skiboot,legoater/skiboot,legoater/skiboot,qemu/skiboot,open-power/skiboot,qemu/skiboot,shenki/skiboot,stewart-ibm/skiboot,legoater/skiboot,qemu/skiboot,open-power/skiboot,shenki/skiboot,open-power/skiboot,legoater/skiboot,qemu/skiboot,legoater/skiboot