Input: atmel_mxt_ts - correct sysfs permissions

Update access permissions of sysfs attributes to macros instead of
hardcoded values. Also correct the permissions of secure_touch_enable
sysfs attribute to write for owner and group only.

Change-Id: I06c5343e0435ddf780ee2423c397198a4a7c89d4
CRs-Fixed: 593775
Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>