Input: lifebook - work properly on Panasonic CF-18

Panasonic CF18 has an active multiplexing controller with
touchscreen connected to one port and a touchpad to another.
Use "phys" from serio port to activate lifebook protoocol
only on the port that has touchscreen connected to it.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>