platform/x86: Toshiba WMI Hotkey Driver

Toshiba laptops that feature WMI events for hotkeys were left unsupported
by the toshiba_acpi driver, however, commit a88bc06e ("toshiba_acpi:
Avoid registering input device on WMI event laptops") added hardware
support for such laptops, but the hotkeys are not handled there.

This driver adds support for hotkey monitoring on certain Toshiba laptops
that manage the hotkeys via WMI events instead of the Toshiba
Configuration Interface (TCI).

The toshiba_acpi driver and this one can co-exist, as this only takes
care of hotkeys, while the proper takes care of hardware related stuff.

Currently the driver is under the EXPERIMENTAL flag, as the keymap
and the notify function are incomplete (due to lack of hardware to test).

Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>