input: atmel_mxt: configure i2c mode gpio for Atmel touch controller

I2C mode is used to serve as a backup for i2c pull up. It can be used to
pull up i2c bus lines when there is no hardware pull-up. Change requires
pulling up i2c mode when touch controller powers on and pulling down
when powering off.

Change-Id: I5c41836d185398d3df2323e90226f6c70fb3d43f
Signed-off-by: Chun Zhang <chunz@codeaurora.org>