Input: atmel_mxt_ts - get rid of qt602240 prefixes in names

Change prefixes from qt602240 to mxt to reflect that the driver supports
whole line of mXT touchscreens.

Signed-off-by: Iiro Valkonen <iiro.valkonen@atmel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>