Allwinner FEL button support
Allwinner FEL button support

Long FEL button press (more than roughly 1 second) is registered
as KEY_ENTER and short FEL button press is registered as KEY_DOWN.
Only works when having root privileges for accessing the hardware
registers via /dev/mem.

This allows to successfully use the dialog menu on any Allwinner
hardware, regardless of the presence/absence of USB ports or any
other conventional input methods. The only requirement is the
availability of the hardware FEL button, which is typically used
for firmware recovery/update on these devices.

Signed-off-by: Siarhei Siamashka <7555503cb5aac63adfd3a7d90e098b88fda217d4@gmail.com>

ssvb/dialog-sunxi,ssvb/dialog-sunxi,ssvb/dialog-sunxi