dt-bindings: arm: fsl: Add i.MX8MM-EVKB

Add DT compatible for the imx8mm EVKB [1].

[1] https://www.nxp.com/design/development-boards/

 \
	i-mx-evaluation-and-development-boards/ \
	evaluation-kit-for-the-i-mx-8m-mini-applications-processor:8MMINILPD4-EVK

Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>
[m.felsch@pengutronix.de: Adapt the commit message]
[m.felsch@pengutronix.de: Adapt the yaml comment]
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>