Revert "x86: Convert MMC to driver model"

Revert "x86: Convert MMC to driver model"

This reverts commit ddb3ac3c716f56cead695444e65a7ba7b0946555.

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>