Integrate meta-guf-distro/cherry-pick-a9d370f1

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Commit: https://git.seco.com/seco-ne/yocto/layers/meta-guf-distro/-/commit/c0d384cc97a5d042a1de31545582da45ff978ced

fng-install:u-boot: Fix installation on devices without u-boot environment

The install script backups some variables from the existing u-boot
environment before overwriting it. This failed for devices where no
environment was available yet, which lead to stop the update with error.
This case is now ignored and the installation continues without backup
in this case.


(cherry picked from commit a9d370f1225eebe42f367b7f3ae454b52a8961cb)