mmc: tegra: use mmc_of_parse to get the support of standard MMC DT bindings

Updating the sdhci-tegra driver to use mmc_of_parse to support standard
MMC DT bindings. Then we can remove the redundant code that already support
in generic MMC core.

Signed-off-by: Joseph Lo <josephl@nvidia.com>
Tested-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Chris Ball <cjb@laptop.org>