ARM: dts: imx6: Support Savageboard dual

Common savageboard DT file is used for board support.
Add the vendor name and specify the dtb file for i.MX6Q build.

Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Milo Kim <woogyom.kim@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>