imx: imx8mm: Add support for Kontron Electronics SL/BL i.MX8M-Mini boards (N801x)

The Kontron SoM-Line i.MX8MM (N801x) by Kontron Electronics GmbH is a SoM
module with an i.MX8M-Mini SoC, 1/2/4 GB LPDDR4 RAM, SPI NOR, eMMC and PMIC.

The matching evaluation boards (Board-Line) have 2 Ethernets, USB 2.0, HDMI/LVDS,
SD card, CAN, RS485 and much more.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>
Tested-by: Heiko Thiery <heiko.thiery@gmail.com>