synaptics_dsx: added software doubletap2wake (dt2w) functionality

* works by not cutting power from the regulators when the device enters
  suspend mode.
* a special irq handler (in doubletab2wake.c) is registered when suspend
  begins, and unregistered as soon as suspend ends and resume begins.
* dt2w is configurable from system settings
* tolerance regarding the distance of the two taps is configurable at
  compile time
* device vibrates on power on
* software rejects touches on the outer 10% extreme areas of the screen,
  to prevent accidental wakeups from handling

Original author: Dennis Rassmann <showp1984@gmail.com>
Signed-off-by: Christian Ciach <christian.ciach@gmail.com>
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>

Change-Id: I3d113ae0e2af3c94826e512b406bf34dfd58496c

drivers/input/touchscreen/Kconfig

@@ -1073,4 +1073,7 @@ config TOUCHSCREEN_IT7260_I2C
 	  To compile this driver as a module, choose M here: the
 	  module will be called it7258_ts_i2c.
 
+config TOUCHSCREEN_DOUBLETAP2WAKE
+	tristate "DoubleTap2Wake for touchscreens"
+	default n
 endif

drivers/input/touchscreen/Makefile

@@ -6,6 +6,8 @@
 
 wm97xx-ts-y := wm97xx-core.o
 
+obj-$(CONFIG_TOUCHSCREEN_DOUBLETAP2WAKE)	+= doubletap2wake.o
+
 obj-$(CONFIG_TOUCHSCREEN_88PM860X)	+= 88pm860x-ts.o
 obj-$(CONFIG_TOUCHSCREEN_AD7877)	+= ad7877.o
 obj-$(CONFIG_TOUCHSCREEN_AD7879)	+= ad7879.o