generate_boot_bins.sh: add support for efiesp modification

[Ananthu C V (WeepingClown13)]

In WP meta, efiesp.bin is where kernel, ramfs, and dtb are packed. We need to enable kernelci jobs for WP based devices and since this scripts handles similar logic, this is by far the best place to handle an image generation. The added efiesp command currently simply modifies an existing base efiesp (which is an easier option than taking a systemd-boot efi and regenerating everything around it) with the necessary files. It assumes a suitable cmdline in a specific format is present in a specific location. This can be enhanced later if necessary to provide custom cmdline arguments, but it is not a necessity at the moment given there is only one consumer. This will help with the immediate requirement of enabling kernelci jobs for WP meta running devices.

EDIT: since this is needed for kernelci, it'll require a new version of docker image released for ci usage.

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