platform/chrome: chromeos_laptop - Add Elan touchpad for Wolf

The upcoming Elan Wolf (Dell Chromebook 11) devices need to know to look
for Elan touchpads on the i2c bus so that they will be functional.

Based on the chromeos-kernel commit :
https://chromium-review.googlesource.com/198283Signed-off-by: NCharlie Mooney <charliemooney@chromium.org>
Signed-off-by: NBenson Leung <bleung@chromium.org>
Signed-off-by: NOlof Johansson <olof@lixom.net>

drivers/platform/chrome/chromeos_laptop.c

@@ -461,6 +461,8 @@ static struct chromeos_laptop dell_chromebook_11 = {
 	.i2c_peripherals = {
 		/* Touchpad. */
 		{ .add = setup_cyapa_tp, I2C_ADAPTER_DESIGNWARE_0 },
+		/* Elan Touchpad option. */
+		{ .add = setup_elantech_tp, I2C_ADAPTER_DESIGNWARE_0 },
 	},
 };