Rework the driver to probe the MMC controller from Device Tree
and make it mandatory. There is no longer support for probing
from the ancient qts-generated header files.

This patch now also removes previous temporary workaround.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Cc: Tom Rini <trini@konsulko.com>