Input: Add support of Synaptics Clickpad device

The new type of touchpads can be detected via a new query command
0x0c. The clickpad flags are in cap[0]:4 and cap[1]:0 bits.

When the device is detected, the driver now reports only the left
button as the supported buttons so that X11 driver can detect that
the device is Clickpad. A Clickpad device gives the button events
only as the middle button. The kernel driver morphs to the left
button. The real handling of Clickpad is done rather in X driver
side.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>