ARM: dts: gemini: Indent DIR-685 partition table

It is discouraged to have OF partitions as subnodes directly
under the device, create a "partitions" subnode and put the
partitions inside it.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>