ARM: kirkwood: provide pinctrl default to sdio nodes

SDIO controllers found on Marvell Kirkwood 6281/6282 SoCs require
pins to be muxed by pinctrl. As there is only one sane pinctrl
setting for this, provide default pinctrl properties to the controller
nodes.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>