thinkpad-acpi: simplify module autoloading

Simplify the module autoloading a great deal, by keying to the HID for
the HKEY interface.

Only _really_ ancient IBM ThinkPad models like the 240, 240x and 570
lack the HKEY interface, and they're getting their own trimmed-down
driver one of these days.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>