arm: imx8m: add support for Compulab iot-gate-imx8 (imx8mm-cl-iot-gate)

Add initial support for Compulab iot-gate-imx8 board (imx8mm-cl-iot-gate).
The initial support includes:
 - MMC
 - eMMC
 - I2C
 - FEC
 - Serial console

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>