Draft: RFC: add package that installs grub-efi images

This generates grub efi application images for multiple archs, and allows installing a grub efi image on a host with a different arch (e.g. x86 efi app on x86_64 system)

I'm pretty sure that using arch="any", etc is not the best way to package this, so I'm open to suggestions.

Also, maybe something like this would fit better in Alpine, but I wanted to make the MR here so we can discuss it more.

This depends on https://gitlab.com/postmarketOS/boot-deploy/-/merge_requests/27, this branch includes a boot-deploy APKBUILD patch to build boot-deploy with the branch in that MR.

This also requires a pmbootstrap patch.

I'm not happy with how deviceinfo vars for boot stuff have been handled (using generate in the name for those vars is kinda misleading, imho). I would much rather use some format for those vars like: deviceinfo_<bootloader>_<bootloader-specific config used by bootdeploy>, and so I used new vars with this format in both the patch here, the changes in boot-deploy, and the patch in pmbootstrap that I'll submit on the mailing list shortly.

The motivation for this is to simplify how pmOS configures x86 and x86_64 systems that use EFI boot. With this change, device packages will no longer need to provide a grub.cfg, or generate a grub EFI app image. boot-deploy is able to also properly inject kernel cmdline params from deviceinfo too (currently device packages that provide a grub.cfg are hard-coding kernel cmdline params...)

pmbootstrap patch: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/%3C20230507022014.25135-1-clayton%40craftyguy.net%3E