mmc: sdhci-of-arasan: Add support for DLL reset for ZynqMP platforms

The DLL resets are required while executing the auto tuning procedure in
ZynqMP. This patch adds code to support the same.

Signed-off-by: Manish Narani <manish.narani@xilinx.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/1579602095-30060-4-git-send-email-manish.narani@xilinx.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>