ARM: dts: vf610: add SD node to cosmic dts

Driver has been there since a while back, but the dts never seems to
have been updated with the node (nor pinctrl). Do so now.

Cc: Matt Porter <mporter@linaro.org>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Olof Johansson <olof@lixom.net>