plankton: Add controls for USB-C port

This CL adds controls for USB-C port:
 - usbc_role: 5V source / 12V source / sink
 - usbc_mux: USB / DP
 - usbc_polarity: CC1 / CC2

BUG=None
TEST=Set/get each control. Check plankton gets the command.

Change-Id: I7edab645f33ffb8858dbc1854dcd8bc3b0360293
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/209367
Reviewed-by: Todd Broch <tbroch@chromium.org>
3 files changed