Input: add support for TI Touchscreen controller

This patch adds support for TI's touchscreen
controller for a 4/5/8 wire resistive panel
that is directly fed to the ADC.

This touchscreen controller will be part of
AM335x TI SoC. The TRM can be found at:
http://www.ti.com/lit/ug/spruh73a/spruh73a.pdf



Signed-off-by: Patil, Rachna <rachna@ti.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>