eglfs: Associate keyboard, touch device with window

Add an optional "keyboardDevice" and "touchDevice" field in QT_QPA_EGLFS_CONFIG and make an association between the device and the window under the given output. If QT_QPA_EGLFS_CONFIG specifies "keyboardDevice" or "touchDevice" for a certain output then the keyboard or touch handler for that device will have a reference to a window which belongs to that output. Then all events handled there will be delivered to that window directly. A handler added later will also be associated to the window if it refers
to the same device node.