input: synaptics_dsx_2.6: creation of secure touch sysfs ifiles

This patch creates two sysfs files for secure touch - secure_touch
and secure_touch_enable, which will be accessed by secure UI app.
We also define the store and show function for these sysfs files.

CRs-Fixed: 990820
Change-Id: Id43118120d4a1f0682904f48b3584d3ba62ef1dd
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>