CHROMIUM: i2c: wire the smart battery passthrough

CHROMIUM: i2c: wire the smart battery passthrough

On Spring, the smart battery is behind the EC.
We are connecting the regular SBS I2C driver and translating i2c
messages for the smart battery to the matching EC commands.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
BUG=chrome-os-partner:17812
TEST=on Spring, read the battery status by using "power-supply-info"
command.

Change-Id: I4d1353d740201935e1bb9566a08f1a81b0262232
Reviewed-on: https://gerrit.chromium.org/gerrit/43610
Reviewed-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>