UEFI: How to go about updating the ESP with loader.efi during installworld

[Rebecca Cran]

I'm currently working on creating and updating the ESP (EFI System Partition) 
for UEFI booting during installation and installworld. 

During installation, with my changes it gets mounted on /boot/efi and loader.efi 
copied into /boot/efi/EFI/FreeBSD and /boot/efi/EFI/BOOT. An entry gets added to 
/etc/fstab as noauto.

The issue comes during installworld, where we'll need to update the loader, 
and I'm not sure how we should handle that. 
If NO_ROOT isn't defined, do we just "mount /boot/efi", overwrite the files then 
unmount it? What should we do if NO_ROOT _is_ defined?

-- 
Rebecca