Comment 4 for bug 1868553

So, "dpkg-reconfigure grub-efi-amd64" now has a screen that matches what
we'd get reconfiguring the old grub-pc:

 ┌──────────────────────┤ Configuring grub-efi-amd64 ├───────────────────────┐
 │ The grub-efi package is being upgraded. This menu allows you to select │
 │ which EFI system partions you'd like grub-install to be automatically │
 │ run for, if any. │
 │ │
 │ Running grub-install automatically is recommended in most situations, to │
 │ prevent the installed GRUB core image from getting out of sync with GRUB │
 │ modules or grub.cfg. │
 │ │
 │ GRUB EFI system partitions: │
 │ │
 │ [*] /dev/sda1 (199 MB; /boot/efi) on 120034 MB INTEL_SSDSC2BW12 │
 │ │
 │ │
 │ <Ok> │
 │ │
 └───────────────────────────────────────────────────────────────────────────┘

I'll test with a system with two ESPs later, but this ought to do the right
thing. You'll need one entry for each, just as you would with an old-meta-
data MD-RAID1 used as an ESP, but as vorlon's noting, this will be a little
safer in the face of UEFI firmware that writes stuff to the drives.

It'd be something like:

efibootmgr -c -d /dev/sda -L ubuntu0 -l '\EFI\UBUNTU\SHIMX64.EFI'
efibootmgr -c -d /dev/sdb -L ubuntu1 -l '\EFI\UBUNTU\SHIMX64.EFI'

This is a win, and I have no further desire for direct MD-RAID 1 support.