Ryu: Add support for the SPI over USB bridge

This enables the USB SPI bridge and adds Ryu specific
functions for enabling and disabling the SPI bridge.

Signed-off-by: Anton Staaf <robotboy@chromium.org>

BRANCH=None
BUG=None
TEST=make buildall -j
     Verify that a modified flashrom can read and write
     the AP SPI Flash.

Change-Id: I3ed2503e23c360c0de7a3aedd1d256be7e82df1e
Reviewed-on: https://chromium-review.googlesource.com/260965
Trybot-Ready: Anton Staaf <robotboy@chromium.org>
Tested-by: Anton Staaf <robotboy@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
Commit-Queue: Anton Staaf <robotboy@chromium.org>
3 files changed