dt-bindings: arm: fsl: add toradex,colibri-imx6ull-emmc

Add toradex,colibri-imx6ull-emmc for our new Colibri iMX6ULL 1GB (eMMC)
Module and the carrier boards (so far only Colibri Evaluation Board) it
may be mated in.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>