Input: cypress_ps2 - don't report as a button pads

The cypress PS/2 trackpad models supported by the cypress_ps2 driver
emulate BTN_RIGHT events in firmware based on the finger position, as part
of this no motion events are sent when the finger is in the button area.

The INPUT_PROP_BUTTONPAD property is there to indicate to userspace that
BTN_RIGHT events should be emulated in userspace, which is not necessary
in this case.

When INPUT_PROP_BUTTONPAD is advertised userspace will wait for a motion
event before propagating the button event higher up the stack, as it needs
current abs x + y data for its BTN_RIGHT emulation. Since in the
cypress_ps2 pads don't report motion events in the button area, this means
that clicks in the button area end up being ignored, so
INPUT_PROP_BUTTONPAD actually causes problems for these touchpads, and
removing it fixes:

https://bugs.freedesktop.org/show_bug.cgi?id=76341

Reported-by: Adam Williamson <awilliam@redhat.com>
Tested-by: Adam Williamson <awilliam@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>