Move all MT-related things to a separate place. This saves some
bytes for non-mt input devices, and prepares for new MT features.
Reviewed-and-tested-by: NBenjamin Tissoires <benjamin.tissoires@enac.fr>
Tested-by: NPing Cheng <pingc@wacom.com>
Acked-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: NHenrik Rydberg <rydberg@euromail.se>