Tegra: MMC: Add DT support to MMC driver for all T20 boards

Tegra: MMC: Add DT support to MMC driver for all T20 boards

tegra_mmc_init() now parses the DT info for bus width, WP/CD GPIOs, etc.
Tested on Seaboard, fully functional.

Tamonten boards (medcom-wide, plutux, and tec) use a different/new
dtsi file w/common settings.

Signed-off-by: Tom Warren <twarren@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Reviewed-by: Stephen Warren <swarren@nvidia.com>