Input: usbtouchscreen - add support for Zytronic capacitive touchscreen

Zytronic USB-attached capacitive touchscreen support within the generic
USB touchscreen driver.

Signed-off-by: Daniel Silverstone <dsilvers@simtec.co.uk>
Signed-off-by: Vincent Sanders <vince@simtec.co.uk>
Signed-off-by: Simtec Linux Team <linux@simtec.co.uk>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>