Read cpusets and max CPU frequencies from devfs and sysfs.

Cpuset information and max CPU frequencies don't change after system bootup.
So, read them only once during init.

If these information are not available, the reader cannot generate CPU info.
So, disable the collector when these cannot be read.

Unit tests are added in one of the following changes.

Test: m
Bug: 217422127
Bug: 242722241

Change-Id: Icc201b65fdfe054da5258e8136750d518182d207
(cherry picked from commit 6a9c8e6063dc8503be23f6f9d94b5a04fafe0c09)