ARM: dts: imx6: Support Savageboard quad

Use common board file and support SATA interface additionally.
Specify the dtb file for i.MX6 build.

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