acer-wmi: set the touchpad toggle key code to KEY_TOUCHPAD_TOGGLE

Set the touchpad toggle key code from F22 to KEY_TOUCHPAD_TOGGLE,
and userspace should use udev's key re-mapping facilities while X
is unable to process keycodes above 255 to adjust to the keycode.

Cc: Matthew Garrett <mjg@redhat.com>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Lee, Chun-Yi <jlee@novell.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>