arm: dts: add imx8mm-cl-iot-gate dts file

Add board dts for imx8mm-cl-iot-gate

Signed-off-by: Kirill Kapranov <kirill.kapranov@compulab.co.il>
Signed-off-by: Uri Mashiach <uri.mashiach@compulab.co.il>
Signed-off-by: Valentin Raevsky <valentin@compulab.co.il>
Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Cc: Peter Robinson <pbrobinson@gmail.com>