mmc: dw_mmc: Probe the MMC from OF

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>