Add sweetberry (consumer hardware power measurement board) firmware support.
This board has an stm32f446 mcu and INA231 current measurement. It supports data acquisition via USB.
feature requirements for sweetberry:
* The timestamp column to be in milliseconds instead of seconds.
* Ability to sync sweetberry clock with the host's, as 64 bit timestamp
* Ability to have multiple sweetberries connected to the same host.
Comment 1 by bugdroid1@chromium.org
, Aug 17 2016