arm: mvebu: add DT information for the SDIO interface of Armada 370/XP

Now that the mvsdio MMC driver has a Device Tree binding, we add the
Device Tree informations to describe the SDIO interface available in
the Armada 370/XP SoCs.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>