Power and volume button support for 5th and 6th generation Microsoft
Surface devices via soc_button_array.

Note that these devices use the same MSHW0040 device as on the Surface
Pro 4, however the implementation is different (GPIOs vs. ACPI
notifications). Thus some checking is required to ensure we only load
this driver on the correct devices.
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>