pass target arch to final image builder as TARGETARCH; use TARGETARCH…

[deitch]

… when generating raw and iso, fallback to build arch; use updated images that read TARGETARCH; ensure grub has EFI for all archs

- What I did

Fixes #3949

When you build for an EFI format for an arch different than the build arch, ensure you get the right .EFI file.

To enable it, it needs to:

• pass the target arch to outputImg() and outputIso(), which pass them to dockerRun(), which passes them via -e to the docker image
• separate grub into 2 packages: grub-dev and grub. It is really hard to cross-build grub's .EFI files. Well, it is easy, but you need the modules, which is not so easy, so it was easier to build grub-dev as images on each target platform and then grub just takes the output .EFI from each
• added a util to canonicalize arch names for go and for march

- How I did it

Changed lots of files, see description above

- How to verify it

CI. Plus I ran local and cross-builds, and they all work correctly.

- Description for the changelog

Handle EFI bootable images for cross-builds