Update cpuinfo to avoid reporting error when sysfs is not accessible (#16107)

Update cpuinfo to avoid reporting error when sysfs is not accessible (#16107)

Summary:
On some cloud-based x86 systems /sys/ is not mounted.
cpuinfo has a work-around for these systems, but it reports an error if sysfs files fail to read, and this error was confusing to some users (e.g. pytorch/cpuinfo#20). This update downgrades the error to a warning, so it is not reported with default configuration options.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16107

Differential Revision: D13715243

Pulled By: soumith

fbshipit-source-id: f5c4c86422343ca449487f0185f3a8865ccf3b9d