X11: build again on Linux distros that don't have XInput 2.2

fixed1616ToReal is needed by the XI2 tablet event debugging added in
ecf11d62fc6f57cccf6f3326e768b1c7cabbd0b3, so it needs to be available
if tablet events are supported and XI 2.2 events are not (older Linux
distros).

Change-Id: Id763d585790a9f037abc408dfba4ab5eec6dd421
Task-number: QTBUG-36437
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Reviewed-by: Wolfgang Bremer <wbremer@blackberry.com>