ARM: kirkwood: add mvsdio driver

This patch add Marvell kirkwood MVSDIO/MMC driver
and enable it for Sheevaplugs and OpenRD boards.

Signed-off-by: Gerald Kerma <drEagle@doukki.net>
Reviewed-by: Stefan Roese <sr@denx.de>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>