mmc: sdhci-of-arasan: Skip Auto tuning for DDR50 mode in ZynqMP platform

ZynqMP platform does not perform auto tuning in DDR50 mode. Skip the
same while the card is operating in DDR50 mode.

Signed-off-by: Manish Narani <manish.narani@xilinx.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/1623753837-21035-4-git-send-email-manish.narani@xilinx.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>