arm: dts: mvebu: Migrate to upstream DT for Synology DS116 (Armada 385) board

Enable OF_UPSTREAM to use upstream DT and add marvell/ prefix to the
DEFAULT_DEVICE_TREE in DS116 defconfig. Remove current DTS in
arch/arm/dts/ directory.

Signed-off-by: Tony Dinh <mibodhi@gmail.com>
Acked-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Stefan Roese <sr@denx.de>