Input: synaptics - enable RMI mode for X1 Extreme 2nd Generation

Just got one of these for debugging some unrelated issues, and noticed
that Lenovo seems to have gone back to using RMI4 over smbus with
Synaptics touchpads on some of their new systems, particularly this one.
So, let's enable RMI mode for the X1 Extreme 2nd Generation.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20191115221814.31903-1-lyude@redhat.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/synaptics.c

@@ -177,6 +177,7 @@ static const char * const smbus_pnp_ids[] = {
 	"LEN0096", /* X280 */
 	"LEN0097", /* X280 -> ALPS trackpoint */
 	"LEN009b", /* T580 */
+	"LEN0402", /* X1 Extreme 2nd Generation */
 	"LEN200f", /* T450s */
 	"LEN2054", /* E480 */
 	"LEN2055", /* E580 */