Upgrade Devkit-power to upower.

BUG=chromium-os:15600
TEST=go to chrome://system. expand upower and check
that it is reasonable.

Change-Id: I63a0b10fd127050fdfcc67699cff9d6d678f12aa
Signed-off-by: Benson Leung <bleung@chromium.org>
Reviewed-on: http://gerrit.chromium.org/gerrit/1776
Reviewed-by: Simon Que <sque@chromium.org>