Uboot is built even if uboot is disabled

[tnichols217]

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The multiple usages of builtins.toString pkgs.uboot-rpi-arm64 within default.nix requires nix to build the uboot package even if uboot is disabled.

I'm unsure if this is an intentional decision based on the requirements of this script, but I would recommend making conditionals for uboot related sections of the script to not be included if uboot is disabled

[tstat]

Yes, good thought. It wasn't intentional, just an oversight.