ARM: sunxi: Add sun4i and cubieboard support

This patch adds support for the Cubieboard based on the Allwinner
A10/sun4i SoC. Currently only UART is supported. Other devices
will eventually follow.

Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>