[Merge] ~dannf/grub:tftp-and-img-base into ~ubuntu-core-dev/grub/+git/ubuntu:ubuntu

[Julian Andres Klode]

Review: Approve

The patches look small enough, so LGTM. 

My concern would be regression potential on the EFI one, as our arm patches are somewhat different state than upstream, so it would be good to ensure it's tested on both arm64 and armhf.
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https://code.launchpad.net/~dannf/grub/+git/grub/+merge/393509
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