mmc: sdhci-tegra: Explicitly support Tegra30

Tegra30 differs from Tegra20 in a number of ways. This patch implements a
minimal set of differences in order to get the Cardhu board's SD slot and
eMMC working. Given the diffs between the mainline sdhci-tegra.c and our
downstream versions, I expect we'll eventually need to add many more
differences, hence the seemingly heavy-weight addition of the soc_data
structure.

* Tegra30 doesn't need to override register access to SDHCI_HOST_VERSION or
  SDHCI_INT_ENABLE.

* Tegra30 needs quirk SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Chris Ball <cjb@laptop.org>