mmc: tegra: Add Tegra186 support

The SDHCI controller found on NVIDIA Tegra186 SoCs is very similar to
the one on prior generations of Tegra and can be supported by the same
driver.

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