sunxi: Enable DM_I2C for all sunxi boards

Now that the last users of legacy I2C (outside of SPL) have been
resolved, we can enable DM_I2C at the sunxi architecture level.

Reviewed-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>