gtk+3: add libxi dependency

Without even compile fails:
| In file included from gdkdevice-xi.c:24:0:
| gdkdeviceprivate-xi.h:28:35: fatal error: X11/extensions/XInput.h: No such file or directory

Signed-off-by: Marko Lindqvist <cazfi74@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>