v3/ec: configure I2C buses for DDC

The STM32 has connections to allow it to intercept the DDC I2C
bus. Configure these pins are input/pull-up so that they don't
interfere with the IT68051's DDC bus.

BUG=b:162915510
TEST=N/A

Change-Id: I15b510e9a7002cab2bf09f313fa287c7952c9c4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/chameleon/+/2740634
Tested-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Alexandru M Stan <amstan@chromium.org>
Commit-Queue: Paul Fagerburg <pfagerburg@chromium.org>
3 files changed