cpu: add ppc64le POWER10 detection

Change-ID: Iffd467d0600a6dcec51232d5ca65ea7c4e7cac77
Assisted-By: "claude my eyes right out"
Reviewed-on: https://go-review.googlesource.com/c/sys/+/822324
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Samuel Karp <samuelkarp@google.com>