arm/dt: msm8974: Add device for atmel_mxt_ts touchscreen

Add info to device tree needed for Atmel touch controller
on msm8974, including regulators, gpios and configuration
data.  Set it as a child of i2c-2 because it is a slave
of the bus.

Change-Id: I440840e94e3aa0bfea74dad0e85ecbd4d34958f5
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>