Implement the functions in mmc_legacy.c for driver-model block devices, so
that MMC can use driver model for these. This allows CONFIG_BLK to be enabled
with DM_MMC.
Signed-off-by: Simon Glass <sjg@chromium.org>
Add basic support for MMC, providing a uclass which can set up an MMC
device. This allows MMC drivers to move to using driver model.
Signed-off-by: Simon Glass <sjg@chromium.org>