sunxi: Add i2c support

Add support for the i2c controller found on all Allwinner sunxi SoCs,
this is the same controller as found on the Marvell orion5x and kirkwood
SoC families, with a slightly different register layout, so this patch uses
the existing mvtwsi code.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Acked-By: Prafulla Wadaskar <prafulla@marvell.com>
Acked-by: Heiko Schocher <hs@denx.de>
[ ijc -- updated u-boot-spl-fel.lds ]