kevin: Add tablet mode control
kevin: Add tablet mode control

Allow the detection of tablet mode for sensors and powerd.

BUG=chromium:606718,b:28552512
BRANCH=kevin
TEST=Check with evtest that events are send.
Check sensor data is in lid referal in tablet mode.

Change-Id: I0822e7419ccba01d70bf9327593164c15493fb10
Signed-off-by: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/380377
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec