Input: add driver for Synaptics I2C touchpad

This driver supports Synaptics I2C touchpad controller on eXeda
mobile device. Unfortunaltely it only works in relative mode and
thus is not comaptible with Xorg Synaptics driver.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>