Integrate meta-seconorth-machine/fix_fnginstall_postinstall

Commit: https://git.seco.com/seco-ne/yocto/layers/meta-seconorth-machine/-/commit/93a0f92f7fea49531491125a78e600c90390ce32

bootscripts: Fixed WIC image

The WIC image generation fails if the devicetree file is missing from the deploy directory.

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Commit: https://git.seco.com/seco-ne/yocto/layers/meta-seconorth-machine/-/commit/4c3847e58d4c38f40c9c9e8083dc0c49f6ad3931

fng-install: Fixed post-install for fngsystem

The post-install for fngsystem is running in a temp directory. This directory was missing the new artifacts (devicetree and overlays) to properly run. Further, the combine step of kernel + devicetree was failing for fngsystem, because the fngsystem partition is too small (at least for i.MX8 devices). To work around this, the post-install scripts checks for a "combine_kernel" file in the boot partition and only combines the kernel and the devicetree if the file is present.