mmc: sunxi: Re-enable eMMC HS-DDR modes on Allwinner A80

Now the the HS-DDR mode clock timings have been corrected, we can
re-enable these modes on the A80.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>