platform/x86: intel-vbtn: Add support for dock mode detection

The Dell laptop I have has an ACPI that sends 0xCB and 0xCC on entering
tablet mode.  On exiting tablet mode it sends 0xCA and 0xCD. Based on:

http://www.traby.de/medion/DSDT/dsdt.dsl
https://gist.github.com/jprvita/5737de3cbb670e80973b7d4e51c38ab6
https://osdn.net/projects/android-x86/scm/git/kernel/commits/


7cbe5a330687b851f32dd9f1048a6ce182d0ff44

It appears that 0xCA and 0xCB are about dock mode, which for my
convertible laptop seems questionably tied to whether I've put
the laptop in tablet or laptop mode.  I previously proposed no-oping
0xCA and 0xCB but this revised change attempts to add support for
detecting dock mode--this detection will essentially be broken for
my laptop (the main workaround would be for 0xCA and 0xCB to be used
to provoke a query of the VGBS method that reports the current dock &
tablet mode [which is accurately reported on my laptop but based on
the prior workarounds in the driver it apparently can't be trusted
for all systems]).

Signed-off-by: Matt Delco <delco@chromium.org>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: platform-driver-x86@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: AceLan Kao <acelan.kao@canonical.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>