ARM: dts: imx6dl-colibri: Add support for Toradex Aster carrier board

Add support for Toradex Aster, small form-factor with header compatible
with Arduino Uno and Raspberry Pi (RPi) maker boards.

Additional detail available at
https://www.toradex.com/products/carrier-boards/aster-carrier-board



Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>