mmc: sunxi: Support MMC_DDR52 timing modes

DDR transfer modes include UHS-1 DDR50 and MMC HS-DDR (or MMC_DDR52).
Consider MMC_DDR52 when setting clock delays.

Since MMC high speed mode goes up to 52 MHz instead of 50 MHz for SD,
and this number is visible in the capability macro, increase the
clock rate upper limit to 52 MHz.

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>