Integrate u-boot-seco-imx/d18-dt-split

Commit: edgehog/bsp/nxp/u-boot-seco-imx@85fa791e

[ALL] add default carrier overlay configuration support

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Commit: edgehog/bsp/nxp/u-boot-seco-imx@91c4381e

[ALL] remove unused var DEFAULT_OVERLAY_FILE