Installs both pmbr+gptzfsboot as well as boot1.efifat in separate partitions
The resulting system can be booted with either UEFI or BIOS/CSM.
Preference is controlled by the user's firmware boot settings.
This is now the default for zfsboot installs
PR: 208629
Submitted by: Galael LAPLANCHE <ganael.laplanche@corp.ovh.com> (original version)