mmc: sunxi: Support 8 bit eMMC DDR transfer modes

Allwinner's MMC controller needs to run at double the card clock rate
for 8 bit DDR transfer modes. Interestingly, this is not needed for
4 bit DDR transfers.

Different clock delays are needed for 8 bit eMMC DDR, due to the
increased module clock rate. For the A80 though, the same values for
4 bit and 8 bit are shared. The new values for the other SoCs were from
A83T user manual's "new timing mode" default values, which describes
them in clock phase, rather than delay periods. These values were used
without any modification. They may not be correct, but they work.

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