Support for multitouch touchscreens (support set-mode command)

Add support for the absolute coordinates mode. This is needed to support 
multitouch touchscreens, instead of touchpad's where this driver was intended 
for. This is working perfectly on my sabreLite iMX6 board with a Nit6X 
multitouch touchscreen. All the multitouch events are still working properly. 
Remark: There is no scaling on the absolute input coordinates so both 
resolutions should match.

I modified this driver for multitouch touchscreen, because I couldn't find another xserver driver for multitouch touchscreens. Because I know that this driver does support all the needed gestures that we want to support in our products. 

I'm sending this patch because I think that also others can benefit from it. And other people has the same problems with finding a good multitouch touchscreen driver. 

If you have any questions or what so ever, please contact me.

Best regards,

Jasper Nevens