Revert "x86: Convert MMC to driver model"

Revert "x86: Convert MMC to driver model"

This reverts commit 46be81a112b1180da7d8eb5dae690b2d2220857a.

With MMC converted to driver model, SCSI driver is broken due to
zero address access at (ops->read) in block_dread() function.

The fix (SCSI driver converted to DM) is ready in u-boot-dm branch,
but it is too late for this relese to get that in.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>