Add the embedded LED support

This patch adds the control of the embedded LED on the top-left corner
of new Synaptics devices.  For LED control, it requires the patch to
Linux synaptics input driver,
	https://patchwork.kernel.org/patch/92434/

When a sysfs file /sys/class/leds/psmouse::synaptics exists, the driver
assumes it supports the embeded LED control.

The LED can be controlled via new properties, "Synaptics LED" and
"Synaptics LED Status".

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Add tap-on-LED feature support

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Add LED debugging statements