llkd: ignore frozen processes

verify a process frozen state by reading its frezer cgroup value and
don't consider it as loop-locked if frozen.

Bug: 145698592
Test: llkd_unit_test
Test: Manually froze a few processes and waited for llkd timeout, verifying that
      no processes are killed, no reboot or ramdump occur and no llkd events are
      logged.
Change-Id: Iea02cd86dbd1df0e6658d02581aa4bb9b658f107