ARM: dts: imx6: add new board RIoTboard

add element14s RIoTboard http://www.riotboard.org

 which is an i.MX6Solo
based design targeted at makers.

Signed-off-by: Iain <Paton&lt;ipaton0@gmail.com>
Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>