servod: add sweetberry as servod device.

In crrev.com/c/1051136 we introduce sweetberry to expose its i2c
interface over usb. This change is to leverage that to use sweetberry
as a servod device. It adds the necessary configurations,
and also introduces a sweetberry.py driver, that manages the servod i2c
ports when reading INAs through servod for sweetberry.

BUG=chromium:806148
TEST=sudo servod -c servo_sweetberry_rails.xml
dut-control -p $PORT j2_1_mv
>j2_1_mv:5087.5
CQ-DEPEND=CL:1051212

Change-Id: I06220510e7051bd7c559856a4b5d252e9f723ffc
Reviewed-on: https://chromium-review.googlesource.com/1051214
Commit-Ready: Ruben Rodriguez Buchillon <coconutruben@chromium.org>
Tested-by: Ruben Rodriguez Buchillon <coconutruben@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
6 files changed