mmc: tegra: Use standard SDHCI tuning on Tegra210 and Tegra186

Add a new sdhci_ops struct for Tegra210 and Tegra186 which doesn't
set the custom tuning callback used on previous SoC generations.

Signed-off-by: Aapo Vienamo <avienamo@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>