Input: ALPS - set DualPoint flag for 74 03 28 devices

BugLink: http://bugs.launchpad.net/bugs/1571530

Here we introduce logic in alps_identify to set the ALPS_DUALPOINT flag
for touchpad hardware responding to E7 report with 73 03 28, as is found
in the Dell Latitude E7470.
Tested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Ben Gamari <ben@smart-cactus.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
(cherry picked from commit aeaa881f)
Signed-off-by: Phidias Chiang <phidias.chiang@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/input/mouse/alps.c

@@ -2741,6 +2741,10 @@ static int alps_set_protocol(struct psmouse *psmouse,
 		if (alps_set_defaults_ss4_v2(psmouse, priv))
 			return -EIO;
 
+		if (priv->fw_ver[1] == 0x1)
+			priv->flags |= ALPS_DUALPOINT |
+					ALPS_DUALPOINT_WITH_PRESSURE;
+
 		break;
 	}
 
@@ -2813,6 +2817,9 @@ static int alps_identify(struct psmouse *psmouse, struct alps_data *priv)
 		} else if (e7[0] == 0x73 && e7[1] == 0x03 &&
 			   e7[2] == 0x14 && ec[1] == 0x02) {
 			protocol = &alps_v8_protocol_data;
+		} else if (e7[0] == 0x73 && e7[1] == 0x03 &&
+			   e7[2] == 0x28 && ec[1] == 0x01) {
+			protocol = &alps_v8_protocol_data;
 		} else {
 			psmouse_dbg(psmouse,
 				    "Likely not an ALPS touchpad: E7=%3ph, EC=%3ph\n", e7, ec);