Input: add driver for keyboard on AAED-2000 development board (ARM)

The keyboard is connected via GPIOs to the processor, and scanned
using a column sample register. The hardware provides no debouncing
mechanism, so the state of the keys is read KBDSCAN_STABLE_COUNT
times before being reported to the input layer.

The status of the keys needs to be polled because there is no
interrupt hooked to the lines. A workqueue is used for this.

Signed-off-by: Nicolas Bellido Y Ortega <ml@acolin.be>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>