porting grub2 - how to get arm64 modules available in amd64 PKG_PATH?

Hi,

I have simple GRUB2 port working but I'm trying to figure out how to change
the port to get some part of it to be a kind of 'noarch' as Linux distros do.

My question is, how to get eg. /usr/local/lib/grub/arm64-efi modules which - IIUC -
would need to build on arm64 box "into" amd64 repo, so they are installable via
pkg_add.

The purpose is to be able to configure netbooting on amd64 box for other
hw platforms.

Example (from Linux), I was preparing network boot for IBM POWER8 on EL7/x86_64:

(grub2-mknetdir is x86_64 binary, but modules are for POWER8)

# grub2-mknetdir -d /usr/lib/grub/powerpc-ieee1275 --net-directory=/tftpboot
Netboot directory for powerpc-ieee1275 created. Configure your DHCP server to point to /data/tftp/boot/grub2/powerpc-ieee1275/core.elf

As I said, Linux distros have 'noarch' repos, IIUC we don't use it.
And I did not understand purpose of NO_ARCH in bsd.port.mk.

One can check how are subpackages of GRUB2 built on Fedora:

https://koji.fedoraproject.org/koji/buildinfo?buildID=1051700

One can also see that on an amd64 box they build "variations" of GRUB2.

$ ftp -MVo - https://kojipkgs.fedoraproject.org//packages/grub2/2.02/26.fc29/data/logs/x86_64/build.log | ggrep -Po '^\+ \.\./configure --build.*\K(--with-platform.*--target=[^ ]*)'
--with-platform=efi --target=x86_64-redhat-linux-gnu
--with-platform=efi --target=i386-redhat-linux-gnu
--with-platform=pc --target=x86_64-redhat-linux-gnu

So, even if I would build on an OpenBSD amd64 these 3 variations (and pc/i386 on
an i386 OpenBSD box), I still don't know how to get 'noarch' packages.

Thank you very much for help.

Jiri