MVME177 panic: pmap_enter_ptpage (PR #45915 on 6.x)

In trying to boot NetBSD/mvme68k 6.x on an MVME177 (50MHz 68060)
board, I'm running into the panic mentioned in PR45915.  Increasing
the number of kernel PT pages was the fix for most ports, but there is
a comment about mvme68k:

"This panic message is m68k pmap specific and some ports might still have
the issue. At least mvme68k updates physmem after bootstrap PT page allocation."

I haven't really looked into this beyond reading the PR.  Does anyone
know if this is an easy fix?  My MVME177 has 64MB of memory if that
makes a difference.

Meanwhile I've booted 5.2 and it seems to work well.  Also 'netboot'
from 6.x fails with an illegal instruction message, while the 5.x
version booted fine.

-Andrew