devicetree: add Dragino vendor id

Please see http://www.dragino.com/about/about.html for details.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12881/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>