ARM: dts: msm: Configure I2C mode gpio for Atmel touch controller

I2C mode is used to serve as a backup for i2c pull up. This can be
configured on 8974 Liquid with a specific gpio port. Adding i2c mode
configuration enables and disables this feature.

Change-Id: I2c49fe9c39141a49fa35567a9b53ec5ac163a09c
Signed-off-by: Chun Zhang <chunz@codeaurora.org>