Input: elantech - enable middle button of touchpads on ThinkPad P52

PNPID is better way to identify the type of touchpads.
Enable middle button support on 2 types of touchpads on Lenovo P52.

Cc: stable@vger.kernel.org
Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/elantech.c

@@ -1175,6 +1175,12 @@ static const struct dmi_system_id elantech_dmi_has_middle_button[] = {
 	{ }
 };
 
+static const char * const middle_button_pnp_ids[] = {
+	"LEN2131", /* ThinkPad P52 w/ NFC */
+	"LEN2132", /* ThinkPad P52 */
+	NULL
+};
+
 /*
  * Set the appropriate event bits for the input subsystem
  */
@@ -1194,7 +1200,8 @@ static int elantech_set_input_params(struct psmouse *psmouse)
 	__clear_bit(EV_REL, dev->evbit);
 
 	__set_bit(BTN_LEFT, dev->keybit);
-	if (dmi_check_system(elantech_dmi_has_middle_button))
+	if (dmi_check_system(elantech_dmi_has_middle_button) ||
+			psmouse_matches_pnp_id(psmouse, middle_button_pnp_ids))
 		__set_bit(BTN_MIDDLE, dev->keybit);
 	__set_bit(BTN_RIGHT, dev->keybit);