FB GUI input devices

The framebuffer GUI supports various input devices through the modern Linux Input Subsystem (/dev/input/event*). Both standard mice and touchscreen devices are supported.

Make sure the USE_INPUT_EVENTS macro is defined in fbsup.h so that the events system is enabled for the FB GUI (this may be configurable at runtime sometime).

Since there can be multiple input devices in /dev/input/ you have to specify which device to use using the POINTING_DEVICE environment variable for the mouse and KEYBOARD_DEVICE environment variable for the keyboard

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