npu2: Add performance tuning SCOM inits
npu2: Add performance tuning SCOM inits

Peer-to-peer GPU bandwidth latency testing has produced some tunable
values that improve performance. Add them to our device initialization.

File these under things that need to be cleaned up with nice #defines
for the register names and bitfields when we get time.

A few of the settings are dependent on the system's particular NVLink
topology, so introduce a helper to determine how many links go to a
single GPU.

Signed-off-by: Reza Arbab <4c896a97e6b998365c2d50a267b0f1ca5f7995de@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

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