modules: flash-script: Add coreutils to updateFirmware script

[hacker1024]

Description of changes

Add coreutils to the updateScript for cat and echo.

updating systemd-boot from 256.7 to 257.2
Copied "/nix/store/2bxf2a2215zspixdmw03vyi31q098ij6-systemd-257.2/lib/systemd/boot/efi/systemd-bootaa64.efi" to "/boot/EFI/systemd/systemd-bootaa64.efi".
Copied "/nix/store/2bxf2a2215zspixdmw03vyi31q098ij6-systemd-257.2/lib/systemd/boot/efi/systemd-bootaa64.efi" to "/boot/EFI/BOOT/BOOTAA64.EFI".
Created EFI boot entry "Linux Boot Manager".
/nix/store/zv8x2rf4lx3fs8pdhpzdhx3wxysr8m6x-update-jetson-firmware/bin/update-jetson-firmware: line 25: cat: command not found
Failed to install bootloader
warning: error(s) occurred while switching to the new configuration

Testing

TODO:

• Check that this actually works

[danielfullmer]

echo is a shell builtin, but this is still needed for cat.