dragon: power: Limit charging to 5V during interactive.

Signed-off-by: Todd Broch <tbroch@google.com>

BUG=chrome-os-partner:43285
TEST=manual,
Via twinkie's vbus measuring capabilities see voltage at 5V when
'interactive' and 12V otherwise when charging with zinger.

Change-Id: Ib76dbec9392c0ccf70ac7231252babcf35a7d8f0
2 files changed