mmc: sdhci-tegra: Add runtime PM and OPP support

The SDHCI on Tegra belongs to the core power domain and we're going to
enable GENPD support for the core domain. Now SDHCI must be resumed using
runtime PM API in order to initialize the SDHCI power state. The SDHCI
clock rate must be changed using OPP API that will reconfigure the power
domain performance state in accordance to the rate. Add runtime PM and OPP
support to the SDHCI driver.

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