power: Log additional info about line power.

This makes powerd log the charger's current and voltage when
available.

BUG=chrome-os-partner:19442
TEST=ran power_supply_info and looked at logs with various
     chargers connected

Change-Id: If0d2ac509aed909348123cb9498e57f589dda360
Previous-Reviewed-on: https://gerrit.chromium.org/gerrit/60943
Reviewed-on: https://gerrit.chromium.org/gerrit/61384
Commit-Queue: Daniel Erat <derat@chromium.org>
Reviewed-by: Daniel Erat <derat@chromium.org>
Tested-by: Daniel Erat <derat@chromium.org>
4 files changed