sunxi: a10-cubieboard: Add user LEDs to the device tree

Cubieboard has two LEDs available for use, a blue one (labeled LED1)
and a green one (labeled LED2).

Signed-off-by: Emilio López <emilio@elopez.com.ar>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>