thinkpad_acpi: Factor out get/set adaptive kbd mode

Move the getting/setting of the adaptive keyboard mode to separate
functions, so that we can reuse them later through sysfs attributes.

Signed-off-by: Bastien Nocera <hadess@hadess.net>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>