ARM: dts: imx7-colibri: add support for Toradex Aster carrier board

Add support for the Toradex Aster carrier board.

Follow the usual hierarchic include model, maintaining shared
configuration imx7-colibri-aster.dtsi.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>