I'm pretty sure we no longer need this, and we don't really need to boot old kernels.
In an ideal world, we'd set some flag, but there's no flag value other than != 0
While we used to return the 1.2MB Floppy geometry for unknown / in valid
drives, that's not checked in any meaningful way in the kernels I looked at.
They are fine being 0 for any kernel any normal person (and like any extreme
special case / extreme use people), and there's no need to preserve them and
we wind up saving a few bytes in the process...