dt-bindings: arm: fsl: Rename compatibles for Kontron i.MX8MM SoM/board

This updates the bindings in order to use names for the boards that
follow the latest convention used by Kontron marketing.

By updating we make sure, that we can maintain this more easily in
future and make sure that the proper devicetree can be selected for
the hardware.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>