Input: add driver for AUO In-Cell touchscreens using pixcir ICs

Some displays from AUO have a so called in-cell touchscreen, meaning it
is built directly into the display unit.

Touchdata is gathered through PIXCIR Tango-ICs and processed in an
Atmel ATmega168P with custom firmware. Communication between the host
system and ATmega is done via I2C.

Devices using this touch solution include the Dell Streak5 and the family
of Qisda ebook readers.

The driver reports single- and multi-touch events including touch area
values.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>