arm64: dts: Add the Kontron i.MX8M Mini SoMs and baseboards

Kontron Electronics GmbH offers small and powerful SoMs based on the
i.MX8M Mini SoC including PMIC, LPDDR4-RAM, eMMC and SPI NOR.

The matching baseboards have the same form factor and similar interfaces
as the other boards from the Kontron "Board-Line" family, including
SD card, 1G Ethernet, 100M Ethernet, USB Host/OTG, digital IOs, RS232,
RS485, CAN, LVDS or HDMI, RTC and much more.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>