Input: Add Microchip AR1021 i2c touchscreen

This patch adds support for the ar1021 i2c based touchscreen.
The driver is quite simple and only supports the Touch
Reporting Protocol.

This is the final version for an RFC patch send a while ago.
http://www.spinics.net/lists/linux-input/msg29419.html

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>