touchpad: release all button presses on device suspend

This leaves a bug open, on a Lenovo T440 generation touchpad with top software
buttons, the button will not be leased correctly. This is caused by
device->is_suspended=true by the time we try to clear the state and the
button events thus getting filtered.

This used to affect all touchpads, this patch just moves it so it only affects
the T440-like devices now.

Fixes #233

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>