mmc: sdhci-of-arasan: Added workaround for auto tuning.

mmc: sdhci-of-arasan: Added workaround for auto tuning.

This patch adds new workaround for auto tuning and
removed existing workaround.
New workaround:
1.The "execute tuning" clears the host controller tuning
circuit and resets the tap values to zero.
2.This reset of the tap value takes a few clock cycles so
wait for few cycles ~60 cycles.
3.Reset the DLL to load an newly updated zero tap value.
4.Send CMD19/CMD21 as a part of the auto tuning process.
5.Once the auto tuning process gets completed.
6.Reset the DLL to load the newly obtained SDHC tuned tap value.

Signed-off-by: Sai Krishna Potthuri <lakshmis@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>