Input: ALPS - fix two-finger scroll breakage in right side on ALPS touchpad

Fixed the issue that two finger scroll does not work correctly
on V8 protocol. The cause is that V8 protocol X-coordinate decode
is wrong at SS4 PLUS device. I added SS4 PLUS X decode definition.

Mote notes:
the problem manifests itself by the commit e7348396c6 ("Input: ALPS
- fix V8+ protocol handling (73 03 28)"), where a fix for the V8+
protocol was applied.  Although the culprit must have been present
beforehand, the two-finger scroll worked casually even with the
wrongly reported values by some reason.  It got broken by the commit
above just because it changed x_max value, and this made libinput
correctly figuring the MT events.  Since the X coord is reported as
falsely doubled, the events on the right-half side go outside the
boundary, thus they are no longer handled.  This resulted as a broken
two-finger scroll.

One finger event is decoded differently, and it didn't suffer from
this problem.  The problem was only about MT events. --tiwai

Fixes: e7348396c6 ("Input: ALPS - fix V8+ protocol handling (73 03 28)")
Signed-off-by: Masaki Ota <masaki.ota@jp.alps.com>
Tested-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Paul Donohue <linux-kernel@PaulSD.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/alps.h

@@ -100,6 +100,10 @@ enum SS4_PACKET_ID {
 				 ((_b[1 + _i * 3]  << 5) & 0x1F00)	\
 				)
 
+#define SS4_PLUS_STD_MF_X_V2(_b, _i) (((_b[0 + (_i) * 3] << 4) & 0x0070) | \
+				 ((_b[1 + (_i) * 3]  << 4) & 0x0F80)	\
+				)
+
 #define SS4_STD_MF_Y_V2(_b, _i)	(((_b[1 + (_i) * 3] << 3) & 0x0010) |	\
 				 ((_b[2 + (_i) * 3] << 5) & 0x01E0) |	\
 				 ((_b[2 + (_i) * 3] << 4) & 0x0E00)	\
@@ -109,6 +113,10 @@ enum SS4_PACKET_ID {
 				 ((_b[0 + (_i) * 3] >> 3) & 0x0010)	\
 				)
 
+#define SS4_PLUS_BTL_MF_X_V2(_b, _i) (SS4_PLUS_STD_MF_X_V2(_b, _i) |	\
+				 ((_b[0 + (_i) * 3] >> 4) & 0x0008)	\
+				)
+
 #define SS4_BTL_MF_Y_V2(_b, _i)	(SS4_STD_MF_Y_V2(_b, _i) | \
 				 ((_b[0 + (_i) * 3] >> 3) & 0x0008)	\
 				)