Draft: Secure Boot now supports both x64 and ia32

1 ) These set of commits enable an i386 image to be booted from an x64 secure boot UEFI. Currently the bootia32.efi and grubia32.efi files are in the image. Unfortunately currently the bootx64.efi and grubx64.efi files do not end up in the image so there's no way that image boots in a x64 secure boot UEFI system.

These set of commits would fix this problem.

2 ) Debian 13 is supposed not to have SecureBoot support for i386 so I'm not sure if it's worth improving this. That's why I send this as a draft.

3 ) Also feedback on the last commit (workaround for 928486 bug) is welcome just in case there's a better way of doing the same thing. It's actually 928486 and 936009 bugs the bugs that are workarounded here.

4 ) I haven't done more tests than my usecases... so I'm not sure if it affects the default builds in a negative way. I am willing to test many default builds once it's clear that some of pull request would be get accepted upstream.

5 ) The idea for testing this merge request would be to run something like this from a i386 bookworm system:

lb config --linux-flavours 'amd64:amd64 686'; sudo lb build

The expected behaviour is that it boots in both x64 UEFIs and ia32 UEFIs which it currently doesn't because of the aforementioned missing bootx64.efi and grubx64.efi files.

Waiting for your feedback.

Thank you!