Treat crypto disk like the root disk, both are boot disks

Treat crypto disk like the root disk, both are boot disks

Chosing [W]hole on a GPT disk means it needs non-default `-b' fdisk(8)
to account for existing EFI Sys partitions, whether it modifies an existing
GPT (Apple APFS ISC) or writing a new one.

With 'Encrypt the root disk?' answered postively, the crypto disk instead of
the root disk becomes the boot disk.

Extend the logic to both crypto and root disk, really asking
"is this a boot disk?".

with caspar