Input: cap11xx - add support for various cap11xx devices

There are variants of the cap11xx device with a varying number of
capacitance detection channels.

Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Reviewed-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>