Include firmware related logs in chrome://system

bios_log: coreboot firmware log
eventlog: persistent firmware event log
bios_times: firmware boot times

BUG=none
TEST=Boot ChromeOS, see above new log files in chrome://system
BRANCH=none

Reviewed-on: https://gerrit.chromium.org/gerrit/35952
Tested-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Commit-Ready: Stefan Reinauer <reinauer@chromium.org>

(cherry picked from commit 735547c6e3add7deab81164773e906a325518a66)

Change-Id: Idd5310e1770b1cb3cd3520e2f92c469a97d12ee4
Reviewed-on: https://gerrit.chromium.org/gerrit/38425
Reviewed-by: Simon Arscott <arscott@chromium.org>
Tested-by: Stefan Reinauer <reinauer@google.com>