input: lge_touch_core: Implement Double tap to wake functionality

If enabled, touchscreen is always powered and user may resume
the device with a double tap on the center of the screen.

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>

Conflicts:
	arch/arm/configs/semaphore_mako_defconfig
	drivers/input/touchscreen/lge_touch_core.c