mci: add Marvell Dove SDHCI driver ...

This adds a driver for the SDHCI controller found on Marvell Dove SoCs.
Despite a missing pinctrl driver, corresponding MPP config has to be
set on a per board basis.

This driver was succesfully tested with Solidrun Dove Cubox.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>