platform: chrome: Add Tablet Switch ACPI driver

Add a kernel driver for GOOG0006, an ACPI driver reporting an event when
the tablet switch status changes.

On an ACPI based convertible chromebook check evtest display tablet mode
switch changes:
Available devices:
..
/dev/input/event3:      Tablet Mode Switch
..
Testing ... (interrupt to exit)
Event: time 1484879712.604360, type 5 (EV_SW), code 1 (SW_TABLET_MODE),
value 1
Event: time 1484879712.604360, -------------- SYN_REPORT ------------
Event: time 1484879715.132228, type 5 (EV_SW), code 1 (SW_TABLET_MODE),
value 0
Event: time 1484879715.132228, -------------- SYN_REPORT ------------
...
Check state is updated at resume time when different from suspend time.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Benson Leung <bleung@chromium.org>