Input: alps - v7: fix finger counting for > 2 fingers on clickpads

Protocol v7 uses the middle / right button bits on clickpads to communicate
"location" information of a 3th touch (and possible 4th) touch on
clickpads.

Specifically when 3 touches are down, if one of the 3 touches is in the
left / right button area, this will get reported in the middle / right
button bits and the touchpad will still send a TWO type packet rather then
a MULTI type packet, so when this happens we must add the finger reported
in the button area to the finger count.

Likewise we must also add fingers reported this way to the finger count
when we get MULTI packets.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=86338


Cc: stable@vger.kernel.org # 3.17
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>