mmc: tegra: Add DM_MMC support to Tegra MMC driver

Convert the Tegra MMC driver to DM_MMC. Support for non-DM is removed
to avoid ifdefs in the code. DM_MMC is now enabled for all Tegra builds.

Cc: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>
(swarren, fixed some NULL pointer dereferences, removed extraneous
changes, rebased on various other changes, removed non-DM support etc.)
Signed-off-by: Stephen Warren <swarren@nvidia.com>